Rapid microassays for the measurement of superoxide and hydrogen peroxide production by macrophages in culture using an automatic enzyme immunoassay reader

Two simple semiautomated microassays for the measurement of superoxide (O-2) and hydrogen peroxide (H2O2) production by cultured macrophages (MPs) are described. The measurement of O-2 is based on the reduction of ferricytochrome c as assayed by the increase in its absorbance at 550 nm. Quantitation of H2O2 is based on the horseradish peroxidase (HRPO)-dependent oxidation of phenol red which is assayed by its increased absorbance at 600 nm. MPs are cultured in monolayers in 96-well flat-bottom tissue culture plates and covered with 100 mul amounts per well of either a ferricytochrome c solution containing phenol red and HRPO. Following the addition of an agent eliciting an oxidative burst (OB) and incubation of the plates at 37 degrees C for various time intervals, the changes in the absorbance of ferricytochrome c and phenol red, respectively, are measured directly in the wells of the tissue culture plates with the cells in situ, by using an automatic 8-channel photometer which reads absorbances vertically through individual wells. This instrument, which was originally designed for reading enzyme immunoassays in microtitration plates, can be easily adapted for use in the above test, when fitted with interference filters with wave lengths of 550 nm (for the assay of O-2) and 600 nm (for the assay of H2O2). The principal advantages of this techniques are: the ability to perform the assays directly in the culture plates with cells in situ; the small amounts of cells and reagents needed; its sensitivity and reproducibility; the ease with which kinetic experiments can be done; the large number of samples which can be tested in parallel, and especially the speed and convenience offered by the automated reading and printout of absorbance values.

Recombinant human interleukin 5 is a selective activator of human eosinophil function

Human rIL-5 was found to selectively stimulate morphological changes and the function of human eosinophils. This molecule is thus a prime candidate for the selective eosinophilia and eosinophil activation seen in disease.

Cellular basis of defective sperm function and its association with the genesis of reactive oxygen species by human spermatozoa

Addition of the divalent cation ionophore, A23187, to washed populations of human spermatozoa resulted in a sudden burst of production of reactive oxygen species which peaked within 3-5 min. This activity was dependent upon the presence of calcium in the external medium and was unaffected by the mitochondrial inhibitors, oligomycin, antimycin and rotenone. Studies with scavengers of reactive oxygen species revealed that, while reagents directed against singlet oxygen and the hydroxyl radical were without effect, cytochrome C reduced the response to A23187 by about 50%, suggesting that the superoxide anion radical is a major product of the activated human spermatozoon. The clinical implications of these studies stem from the considerable variation observed between individuals in the levels of reactive oxygen species produced by the spermatozoa. This variability was shown to be inversely related to the ability of the spermatozoa to exhibit sperm-oocyte fusion on exposure to A23187; defective samples exhibited a basal level of reactive oxygen species production which was 40 times that observed with normal functional cells.

Increased superoxide anion production by immunologically activated and chemically elicited macrophages

We studied the capacity of cultured mouse peritoneal macrophages to generate superoxide anion (O(2-)), the initial product of conversion of oxygen to microbicidal species, during phagocytosis of opsonized zymosan or upon contact with the membrane-active agent phorbel myristate acetate (PMA). Macrophages from mice infected with Bacille Calmette-Guerin (BCG) or injected intraperitoneally with thioglycollate broth or endotoxin, released up to 12 times more O(2-) than did resident peritoneal macrophages, depending upon the cell type and whether the stimulus was zymosan or PMA. There was little if any O(2-) release from resting (unstimulated) macrophages. The density of cells on culture dishes was an important variable since crowding of the dish markedly reduced the efficiency of O(2-) production. The enhanced O(2-) release of chemically elicited and infection-activated macrophages was noted after stimulation with a wide range of concentrations of PMA and zymosan, at all time points studied (up to 120 min), and with cells maintained for 140 rain to 16 days in culture. The O(2-) response of resident cells improved twofold to zymosan and ninefold to PMA during the first 3 days in culture. The capacity to release O~ appears to be limited to actively phagocytic cell types: murine macrophage-like tumor lines and cultured human monocytes released O(2-) when stimulated by PMA or zymosan, fibroblast and endothelial lines and embryo-derived cells did not. Activity of superoxide dismutase, which removes O(2-), was not detectable in culture supernates of any cell type, and thus, differences in detectable O(2-) could not be attributed to variations in the release of this enzyme. We conclude that the phagocytosis- associated respiratory burst is significantly enhanced in mononuclear phagocytes obtained ai~r chemical inflammation or BCG infection. Increased capacity to generate O(2-) and other oxygen radicals during phagocytosis could contribute to the improved microbicidal and tumoricidal activity of activated macrophages.

Complement and immunoglobulins stimulate superoxide production by human leukocytes independently of phagocytosis

Human peripheral blood polymorphonuclear leukocytes, when exposed to appropriate stimuli, generate significant amounts of superoxide anion (O-.2), a highly reactive molecule which is possibly involved in bacterial killing. Since the subcellular localization and mechanism of activation of O-.2 generating systems are unknown, we have investigated superoxide dismutase-inhibitable cytochrome c reduction (attributable to O-.2) by, and lysosomal enzyme release from, normal polymorphonuclear leukocytes and cells rendered incapable of ingesting particles by treatment with cytochalasin B. Neither phagocytosis nor lysosomal degranulation were prerequisites for enhanced O-.2 generation. Cytochalasin B-treated cells exposed to (a) serum-treated zymosan, a C3b receptor stimulus; (b) heat aggregated human IgG, an Fc receptor stimulus; and (c) the complement component, C5a, generated enhanced amounts of O-.2 in a time and concentration-dependent fashion. These cells also responded by releasing lysosomal enzymes, but there was no correlation between the ability of any immune reactant to provoke enzyme release and its ability to stimulate O-.2 generation. The three stimuli also enhanced O-.2 generation by normal (untreated) polymorphonuclear leukocytes, but only serum-treated zymosan and aggregated IgG were capable of provoking lysosomal enzyme release from normal cells. Untreated zymosan and native IgG neither stimulated O-.2 production nor provoked lysomal enzyme release. Since enhanced O-.2 production was stimulated by immune reactants in the absence of phagocytosis, the O-.2 generating system is very likely associated with the external plasma membrane of the polymorphonuclear leukocyte. Leukocyte membrane receptors for complement and immunoglobulins may therefore not only serve in particle recognition but also may initiate biochemical events which accompany phagocytosis and killing.

A novel neutrophil-activating factor produced by human mononuclear phagocytes

The biological properties of a neutrophil-activating factor (NAF), which was recently identified as a novel peptide of approximately 6,000 mol wt, are described. NAF is produced de novo by human blood monocytes upon stimulation with LPS, PHA, and Con A. It induces two main responses in human neutrophils, i.e., exocytosis (release from specific granules in normal, and from specific and azurophil granules in cytochalasin B-treated cells) and the respiratory burst (formation of superoxide and hydrogen peroxide). The action of NAF appears to be mediated by a surface receptor as shown by the following observations. (a) NAF induces a rapid and transient rise in cytosolic free Ca2+; (b) interaction with NAF results in desensitization, since the cells do not respond to a second NAF challenge; and (c) the respiratory burst elicited by NAF is similar in onset, and time course to that induced by C5a or FMLP. The NAF receptor can be distinguished from the receptors of C5a, FMLP, platelet-activating factor, and leukotriene B4 by the lack of cross-desensitization. Unlike C5a, the other host-derived neutrophil-activating peptide, NAF is not inactivated by serum and thus presumably accumulates in inflamed tissue.

Highly purified murine interleukin 5 (IL-5) stimulates eosinophil function and prolongs in vitro survival. IL-5 as an eosinophil chemotactic factor

The recent molecular cloning of the complementary DNA encoding T cell--replacing factor (TRF) has demonstrated that a single molecule is responsible for B cell growth factor II (BCGF-II) activity and eosinophil differentiation activity. It has been proposed that this molecule be called interleukin 5 (IL-5). We previously reported that purified rIL-5 supports the terminal differentiation and proliferation of eosinophilic precursors. In this study, we examined the effects of IL-5 on functional activities of mature eosinophils. IL-5 maintained the viability of mature eosinophils obtained from peritoneal exudate cells of mice infected with parasites. It also induced superoxide anion production in a dose-dependent manner. The Boyden's chamber Millipore assay revealed that IL-5 had a marked chemokinetic effect on eosinophils in a dose-dependent manner. Moreover, IL-5 was found to be an eosinophil chemotactic factor by the checkerboard assay. In conclusion, IL-5 is suggested to play an important role in increasing the functional activities of eosinophils as well as their production in allergic and parasitic diseases.

H2O2 release from human granulocytes during phagocytosis. Relationship to superoxide anion formation and cellular catabolism of H2O2: studies with normal and cytochalasin B-treated cells

Normal and cytochalasin B-treated human granulocytes have been studied to determine some of the interrelationships between phagocytosis-induced respiration and superoxide and hydrogen peroxide formation and release into the extracellular medium by intact cells. By using the scopoletin fluorescent assay to continuously monitor extracellular hydrogen peroxide concentrations during contact of cells with opsonized staphylococci, it was demonstrated that the superoxide scavengers ferricytochrome c and nitroblue tetrazolium significantly reduced the amount of H(2)O(2) released with time from normal cells but did not abolish it. This inhibitory effect was reversed by the simultaneous addition of superoxide dismutase (SOD), whereas the addition of SOD alone increased the amount of detectable H(2)O(2) in the medium. The addition of sodium azide markedly inhibited myeloperoxidase-H(2)O(2)-dependent protein iodination and more than doubled H(2)O(2) release, including the residual amount remaining after exposure of the cells to ferricytochrome c, suggesting its origin from an intracellular pool shared by several pathways for H(2)O(2) catabolism. When cells were pretreated with cytochalasin B and opsonized bacteria added, reduced oxygen consumption was observed, but this was in parallel to a reduction in specific binding of organisms to the cells when compared to normal. Under the influence of inhibited phagosome formation by cytochalasin B, the cells released an increased amount of superoxide and peroxide into the extracellular medium relative to oxygen consumption, and all detectable peroxide release could be inhibited by the addition of ferricytochrome c. Decreased H(2)O(2) production in the presence of this compound could not be ascribed to diminished bacterial binding, decreased oxidase activity, or increased H(2)O(2) catabolism and was reversed by the simultaneous addition of SOD. Furthermore, SOD and ferricytochrome c had similar effects on another H(2)O(2)-dependent reaction, protein iodination, in both normal and cytochalasin B cells. When oxygen consumption, O(2.) (-), and H(2)O(2) release were compared in the presence of azide under identical incubation conditions, the molar relationships for normal cells were 1.00:0.34:0.51 and for cytochalasin B-treated cells 1.00:0.99:0.40, respectively. Nonopsonized, or opsonized but disrupted, bacteria did not stimulate any of these metabolic functions. The results indicate that with normal cells approximately 50% of H(2)O(2) released during phagocytosis is derived directly from O(2.) (-) by dismutation, the remainder appearing from an (intra)cellular source shared by azide-inhibitable heme enzymes. With cytochalasin B treatment the evidence is consistent with the derivation of all H(2)O(2) from an O(2.) (-) precursor which is released from the cell surface. Furthermore, when activated by phagocytic particle binding, the neutrophil O(2.) (-) generating system appears to make more of this compound than can be accounted for by dismutation to H(2)O(2). This establishes conditions for the direct participation of both compounds in the microbicidal and cytocidal activity of these cells.

Superoxide generation by digitonin-stimulated guinea pig granulocytes. A basis for a continuous assay for monitoring superoxide production and for the study of the activation of the generating system

Stimulation of guinea pig granolocytes by digitonin results in superoxide (O-2) generation. A continuous assay shows that there is a lag between the addition of digitonin and the onset of O-2 production. The rate of activation of the O-2 generating system is dependent upon the concentration of digitonin and the temperature. The final linear rate of O-2 production is affected by the concentration of digitonin, temperature, pH, and the presence of exogenous reduced pyridine nucleotides. Thus, factors which alter either the activation process or the activity of the O-2 generating system can affect O-2 production by stimulated granolocytes.

The biology and pathology of oxygen radicals

Superoxide radicals (O2-) are commonplace products of the biological reduction of oxygen. Their intrinsic reactivity and ability to generate other more reactive entities constitute a threat to cellular integrity. Superoxide dismutases, enzymes that catalytically scavenge these radicals, have evolved to meet this threat. These metalloenzymes are essential for respiring organisms to survive. Several compounds, such as the antibiotic streptonigrin and the herbicide paraquat, augment the production rate of O2- inside cells. This accounts for the oxygen-enhancement of their lethality. Some bacteria respond to this artificially increased rate of O2- production by synthesizing additional superoxide dismutase. Ionizing radiation generates O2- in its passage through oxygenated aqueous media, and superoxide dismutase added to the suspending medium, decreases the oxygen-enhancement of the lethality of such irradiation of the bacterium Escherichia coli. Production of O2- by activated neutrophils is clinically significant, since it is an important component of the bactericidal actions of these cells and the inflammatory process. Superoxide dismutases exert an anti-inflammatory action that may be useful in managing inflammations.

Inhibition of the inflammatory action of interleukin-1 and tumor necrosis factor (alpha) on neutrophil function by pentoxifylline

Inflammatory cytokines, including interleukin-1 and tumor necrosis factor, are produced by monocytes and macrophages in response to microorganisms and microbial products such as endotoxins. The cytokines stimulate neutrophil adherence, degranulation, and superoxide production but inhibit neutrophil migration. We studied the modulation of cytokine-induced neutrophil activation by pentoxifylline and its principle metabolites. Lipopolysaccharide-stimulated mononuclear-leukocyte-conditioned medium containing inflammatory cytokines, purified human interleukin-1, or recombinant human tumor necrosis factor increased neutrophil adherence to nylon fiber, primed neutrophils for increased superoxide production in response to N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP), increased neutrophil lysozyme release stimulated by FMLP, and decreased directed migration of neutrophils to FMLP. Pentoxifylline and its principle metabolites at or near therapeutically achievable levels were able to counteract these effects. Pentoxifylline inhibited the increase in free intracellular calcium in polymorphonuclear leukocytes stimulated by FMLP and increased binding of FMLP to neutrophils at 37 degrees C but not at 4 degrees C. By blocking the inflammatory action of interleukin-1 and tumor necrosis factor on neutrophils, pentoxifylline may diminish the tissue damage caused by neutrophils in such conditions as septic shock, adult respiratory distress syndrome, cardiopulmonary bypass lung damage, and myocardial reperfusion injury.

Unsaturated fatty acids stimulate NADPH-dependent superoxide production by cell-free system derived from macrophages

Arachidonic acid (C20:4) and other unsaturated fatty acids are shown to activate superoxide (O2-) production in a cell-free system represented by sonically disrupted guinea pig peritoneal macrophages. The reaction requires a heat-sensitive cellular component and NADPH, is enhanced by flavin adenine dinucleotide (FAD), and is not linked to enzymatic oxidation of the fatty acid. C20:4-elicited O2- formation is dependent on the cooperation between a subcellular component sedimentable at 48,000g (probably containing the O2- -forming enzyme) and a cytosolic factor. This appears to be the first report of O2- generation being elicited in a cell-free system derived from unstimulated cells and supports the idea that unesterified unsaturated fatty acids act as second messengers of O2- formation in intact phagocytes.

Chemiluminescence and superoxide production by myeloperoxidase-deficient leukocytes

The role of superoxide anion- and myeloperoxidase-dependent reactions in the light emission by phagocytosing polymorphonuclear leukocytes has been investigated using leukocytes that lack myeloperoxidase, inhibitors (azide, superoxide dismutase), and model systems. Our earlier finding that oxygen consumption, glucose C-1 oxidation, and formate oxidation are greater in polymorphonuclear leukocytes that lack myeloperoxidase than in normal cells during phagocytosis has been confirmed with leukocytes from two newly described myeloperoxidase-deficient siblings. Although the maximal rate of superoxide anion production by myeloperoxidase-deficient leukocytes is not significantly different from that of normal cells, superoxide production falls off less rapidly with time so that with prolonged incubation, it is greater in myeloperoxidase-deficient than in normal cells. Chemiluminescence by myeloperoxidase-deficient leukocytes during the early postphagocytic period however is decreased. Light emission by normal leukocytes is strongly inhibited by both superoxide dismutase and azide, whereas that of myeloperoxidase-deficient leukocytes, while still strongly inhibited by superoxide dismutase is considerably less sensitive to azide. Zymosan, the phagocytic particle employed in the intact cell system, considerably increased the chemiluminescence of a cell-free superoxide-H2O2 generating system (xanthine-xanthine oxidase) and a system containing myeloperoxidase, H2O2, and chloride. Light emission by the xanthine oxidase model system is strongly inhibited by superoxide dismutase and is not inhibited by azide, whereas the myeloperoxidase-dependent model system is strongly inhibited by azide but only slightly inhibited by superoxide dismutase. These findings suggest that light emission by phagocytosing polymorphonuclear leukocytes is dependent on both myeloperoxidase-catalyzed reactions and the superoxide anion, and involves in part the excitation of the ingested particle. These studies are discussed in relation to the role of the superoxide anion and chemiluminescence in the microbicidal activity of the polymorphonuclear leukocyte.

A quantitative fluorimetric assay for the determination of oxidant production by polymorphonuclear leukocytes: its use in the simultaneous fluorimetric assay of cellular activation processes

A fluorimetric assay for the indirect determination of superoxide production during the respiratory burst of stimulated polymorphonuclear leukocytes was described. The method allowed the determination of submicromolar concentrations of superoxide, and was sufficiently sensitive that first-derivative kinetic analysis of the respiratory burst could be quickly analyzed. Conditions for the simultaneous fluorimetric analysis of superoxide production and intracellular calcium fluxes were described.

Two forms of autosomal chronic granulomatous disease lack distinct neutrophil cytosol factors

Chronic granulomatous diseases of childhood (CGD) are a group of disorders of phagocytic cell superoxide (O2.-) production (respiratory burst). Anion exchange chromatography separated from normal neutrophil cytosol a 47-kilodalton neutrophil cytosol factor, NCF-1, that restored activity to defective neutrophil cytosol from most patients with autosomally inherited CGD in a cell-free O2.--generating system. A 65-kilodalton factor, NCF-2, restored activity to defective neutrophil cytosol from one patient with autosomal CGD. NCF-1, NCF-2, and a third cytosol fraction, NCF-3, were inactive alone or in pairs, but together replaced unfractionated cytosol in cell-free O2.- generation. Neutrophils deficient in NCF-1, but not NCF-2, did not phosphorylate the 47-kilodalton protein. It is proposed that NCF-1, NCF-2, and NCF-3 are essential for generation of O2.- by phagocytic cells and that genetic abnormalities of these cytosol components can result in the CGD phenotype.

Adriamycin stimulated superoxide formation in submitochondrial particles

Adriamycin (doxorubicin), an anticancer agent, stimulated the formation of superoxide in submitochondrial particles isolated from bovine heart. Superoxide formation was detected by oxygen uptake, by the cooxidation of epinephrine to adrenochrome and by the reduction of acetylated cytochrome c. These processes were sensitive to superoxide dismutase (SOD). Rotenone-insensitive oxidation of NADH by the mitochondrial respiratory chain in the presence of oxygen caused the formation of approx 4 nmol of superoxide per min/mg of protein. Adriamycin at a concentration of 400 micron stimulated the rate of superoxide formation 6-fold to 25 nmol.min-1.mg-1, but this was not a maximum rate. Approximately 50 micron adriamycin was estimated to be sufficient for obtaining one-half maximal stimulation. Hydrogen peroxide accumulated as a final reaction product. Measurements of the relative catalase activity of blood-free tissues of rabbits and rats indicated that heart contained 2 to 4% of the catalase activity of liver or kidney. An enhanced production of superoxide and hydrogen peroxide and the relatively low catalase content of heart tissue may be factors in the cardiotoxicity induced by adriamycin chemotherapy if a similar reaction occurs in vivo.

Generation of superoxide anion and chemiluminescence by human monocytes during phagocytosis and on contact with surface-bound immunoglobulin G

Extent of O-2-release and chemiluminescence, attributed to singlet oxygen, has been compared in human monocytes and neutrophils during phagocytosis, stimulation by the surface-active agent phorbol myristate acetate, or contact with aggregated IgG in a model of immune complex disease. Monocytes generated O-2-and chemiluminescence with each of the three stimuli, although values were significantly less than those of neutrophils from the same individuals. Lymphocytes had no significant activity in either assay with any stimulus. Oxygen metabolites released from mononuclear phagocytes are highly reactive and could play a part in both the beneficial and detrimental aspects of chronic inflammation.

Evidence that the superoxide-generating system of human leukocytes is associated with the cell surface

Superoxide anion (O-2-) generation by human peripheral blood polymorphonuclear leukocytes is enhanced when these cells encounter appropriate soluble or particulate stimuli. O-2- generation requires intact, viable cells and proceeds independently of phagocytosis. To investigate the possibility that the O-2--generating system is associated with the outer surface of the polymorphonuclear leukocyte plasma membrane, we have examined the effects upon O-2- production of p-diazobenzenesulfonic acid, a reagent which can react predominantly with proteins of the external cell membrane. When normal human polymorphonuclear leukocytes were preincubated with cytochalasin B (to minimize endocytosis) and then exposed to the surface-active lectin, concanavalin A, the cells were stimulated to generate O-2- in a concentration- and time-dependent fashion and selectively to discharge the granule-associated enzyme, lysozyme, into the surrounding medium. These responses, as well as cellular binding of [H] concanavalin A, could be blocked by alpha-methyl-D-mannoside. Brief treatment (less than 5 min at 4 degrees C) of the cells with p-diazobenzenesulfonic acid (1.0-5.0 mM) significantly interfered with concanavalin A-mediated O-2- generation but had no influence upon lysozyme release or upon binding of [3H] concanavalin A. The diazonium salt did not alter cell viability or the specific activity of the cytoplasmic enzyme, lactate dehydrogenase (inhibitable under conditions which allowed entry of this reagent into the cytosol). p-Diazobenzenesulfonic acid, therefore, very likely exerted its effects at the cell surface of the intact polymorphonuclear leukocyte, selectively inhibiting O-2- production (either directly or indirectly) without influencing another response to lectin-cell contact: release of lysozyme. These results support the possibility that a polymorphonuclear leukocyte ectoenzyme is responsible for O-2- production.

Increased chemiluminescence and superoxide production in the liver of chronically ethanol-treated rats

Rats fed ethanol (1.74 +/- 0.12 g/day/100 g body wt for 12 weeks) showed a 45% increased microsomal production of O-2 (2.23 +/- 0.14 nmol/min/mg protein) and a 28% increased content of endoplasmic reticulum protein (26.8 +/- 1.4 mg/g liver). This could lead, at substrate saturation, to a 86% increased cytosolic production of O-2 which is not compensated by cytosolic superoxide dismutase levels that remain normal. It is claimed that this unbalance between O-2 production and superoxide dismutase leads to a peroxidative stress in agreement with the 54% increased spontaneous liver chemiluminescence (37 +/- 2 cps/cm2) measured in the ethanol-treated rats. Hydroperoxide-induced chemiluminescence was 57, 43, and 28% higher, respectively, in homogenates, mitochondria, and microsomes isolated from ethanol-treated rats as compared with controls. Vitamins E and A were more effective inhibitors of the hydroperoxide-stimulated chemiluminescence in the liver homogenates from ethanol-treated rats as compared with the effect on the homogenates from control animals. The results are consistent with a peroxidative stress in chronic alcoholism leading to increased lipoperoxidation and decreased levels of antioxidants.

Reduction of the size of infarction by allopurinol in the ischemic-reperfused canine heart

This study was performed to assess the effect of allopurinol in a canine preparation of myocardial infarction. Dogs underwent occlusion of the left circumflex coronary artery for 90 min, followed by reperfusion for 6 hr. Three groups were studied: (1) control, (2) dogs receiving 25 mg/kg allopurinol 18 hr before occlusion and 50 mg/kg 5 min before occlusion, and (3) dogs receiving allopurinol as above plus 5 mg/kg superoxide dismutase over 1 hr beginning 15 min before reperfusion. Infarct size expressed as a percentage of the area at risk was 40 +/- 4 in the control group, 22 +/- 5 in the allopurinol group (p less than .05 vs control), and 17 +/- 4 in the allopurinol plus superoxide dismutase group (p less than .05 vs control). The differences in infarct size were not due to differences in myocardial oxygen supply or demand. Neutrophil superoxide anion production was not altered by allopurinol treatment. The results suggest that myocardial xanthine oxidase may generate oxygen radicals that play a role in myocardial injury due to ischemia and reperfusion.

Modes of action of aspirin-like drugs

Current dogma holds that nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibition of the synthesis and release of prostaglandins. However, NSAIDs also inhibit the activation of neutrophils, which provoke inflammation by releasing products other than prostaglandins. We now report that NSAIDs (e.g., indomethacin, piroxicam) inhibit activation of neutrophils by inflammatory stimuli, such as C5-derived peptides and leukotriene B4, even when cyclooxygenase products generated in suspensions of stimulated neutrophils (prostaglandin E and thromboxanes) are present. Sodium salicylate (3 mM) greatly inhibited aggregation of neutrophils but had no effect on aggregation of platelets or production of thromboxane induced by arachidonate. Sodium salicylate and other NSAIDs also inhibit calcium movements (45Ca uptake, changes in fluorescence of chlortetracycline and quin-2). Aspirin, sodium salicylate, indomethacin, and piroxicam also enhanced the poststimulation increase in intracellular cyclic AMP. NSAIDs therefore inhibit early steps in neutrophil activation as reflected by their capacity to inhibit movements of Ca and to enhance intracellular levels of cyclic AMP.

Intracellular pH modulates the generation of superoxide radicals by human neutrophils

The relationship of intracellular pH (pHi) to superoxide radical (O2-) generation was investigated in chemotactic factor-stimulated human neutrophils. Exposure of cells to 100 nM N-formylmethionyl-leucyl-phenylalanine (FMLP) caused activation of Na/H exchange which, in 140 mM Na medium (pH0 7.40), led to a rise in pHi from 7.22 to 7.80. This pHi change was sensitive to amiloride (apparent Ki 78 microM), an inhibitor of Na/H countertransport. The time course of the alkalinization was similar to that of FMLP-stimulated O2- production, which was complete by 5 min. In the presence of 1 mM amiloride, which nearly blocked the pHi transient elicited by FMLP, or in the absence of external Na, where intracellular acidification was observed in FMLP-stimulated cells, O2- release was still roughly 25-45% of normal. Thus, an alkalinization cannot be an obligatory requirement for O2- generation. By independently varying either pH0, pHi, or the internal or external concentrations of Na, both the direction and magnitude of the FMLP-induced pHi transients could be altered. In each instance, the amount of O2- release correlated directly with pHi and was enhanced by intracellular alkalinization. In the absence of FMLP, a rise in pHi to 7.7-7.8 by exposure of cells to 30 mM NH4Cl, 10 microM monensin (a Na/H exchanging ionophore), or after a prepulse with 18% CO2 did not result in O2- generation. Thus, these results imply that an alkalinization per se is not a sufficient trigger. Neutrophils exposed to 4 nM FMLP exhibited a threefold slower rate of alkalinization (reaching pHi approximately 7.80 by 20-30 min) as compared to that obtained with 100 nM FMLP and did not release significant amounts of O2- under normal incubation conditions. However, these cells could be induced to generate O2- when the degree of alkalinization was enhanced by internal Na depletion or by pretreatment with 18% CO2. Together, these results indicate a modulating effect of pHi on O2- production and suggest that other functional responses of neutrophils may be regulated by their pHi.

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

N-ethylmaleimide, divalent cations, ethylene glycol bis (beta aminoethyl ether) N,N,N',N',-tetraacetate, 2-deoxyglucose, cyanide, and dinitrophenol were examined for their effect on the ability of guinea pig granulocytes to generate superoxide (O(2) (-)) when stimulated by digitonin. N-ethylmaleimide (1 mM) inhibits only when added before complete activation of the O(2) (-) generating system, and at lower concentrations (0.05-0.2 mM) slows the activation process. Ca(++) is required for maximum O(2) (-) generation, and Mg(++) decreases the amount of Ca(++) required. Ethylene glycol bis (beta aminoethyl ether) N,N,N',N',-tetraacetate (10 mM) inhibits only if added before complete activation. Incubation of cells in 2-DOG causes a time- and concentration-dependent inhibition of O(2) (-) generation. It also increases the time required for activation of this system. Cyanide and dinitrophenol increase the rate of O(2) (-) production. However, when these compounds are added to cells whose O(2) (-) production is partially inhibited by incubation in 2-deoxyglucose, complete inhibition results. If cyanide or dinitrophenol is added after activation of 2-deoxyglucose-treated cells, no further inhibition occurs. On the basis of the above results, we conclude that the activation of the O(2) (-) generating system is N-ethylmaleimide sensitive, Ca(++) dependent, and energy requiring, but that the activity of the enzyme system in the cell is not.