Evidence for hydroxyl radical generation by human Monocytes

Activatable Fluorescent Probe for Studying Drug-Induced Senescence In Vitro and In Vivo

Aging represents a significant risk factor for compromised tissue function and the development of chronic diseases in the human body. This process is intricately linked to oxidative stress, with HClO serving as a vital reactive oxygen species (ROS) within biological systems due to its strong oxidative properties. Hence, conducting a thorough examination of HClO in the context of aging is crucial for advancing the field of aging biology. In this work, we successfully developed a fluorescent probe, OPD, tailored specifically for detecting HClO in senescent cells and in vivo. Impressively, OPD exhibited a robust reaction with HClO, showcasing outstanding selectivity, sensitivity, and photostability. Notably, OPD effectively identified HClO in senescent cells for the first time, confirming that DOX- and ROS-induced senescent cells exhibited higher HClO levels compared to uninduced normal cells. Additionally, in vivo imaging of zebrafish demonstrated that d-galactose- and ROS-stimulated senescent zebrafish displayed elevated HClO levels compared to normal zebrafish. Furthermore, when applied to mouse tissues and organs, OPD revealed increased fluorescence in the organs of senescent mice compared to their nonsenescent counterparts. Our findings also illustrated the probe's potential for detecting changes in HClO content pre- and post-aging in living mice. Overall, this probe holds immense promise as a valuable tool for in vivo detection of HClO and for studying aging biology in live organisms.

Ten "Cheat Codes" for Measuring Oxidative Stress in Humans

Formidable and often seemingly insurmountable conceptual, technical, and methodological challenges hamper the measurement of oxidative stress in humans. For instance, fraught and flawed methods, such as the thiobarbituric acid reactive substances assay kits for lipid peroxidation, rate-limit progress. To advance translational redox research, we present ten comprehensive "cheat codes" for measuring oxidative stress in humans. The cheat codes include analytical approaches to assess reactive oxygen species, antioxidants, oxidative damage, and redox regulation. They provide essential conceptual, technical, and methodological information inclusive of curated "do" and "don't" guidelines. Given the biochemical complexity of oxidative stress, we present a research question-grounded decision tree guide for selecting the most appropriate cheat code(s) to implement in a prospective human experiment. Worked examples demonstrate the benefits of the decision tree-based cheat code selection tool. The ten cheat codes define an invaluable resource for measuring oxidative stress in humans.

The Interplay between Endogenous and Foodborne Pro-Oxidants and Antioxidants in Shaping Redox Homeostasis

Oxidative stress has been known about in biological sciences for several decades; however, the understanding of this concept has evolved greatly since its foundation. Over the past years, reactive oxygen species, once viewed as solely deleterious, have become recognized as intrinsic components of life. In contrast, antioxidants, initially believed to be cure-all remedies, have failed to prove their efficacy in clinical trials. Fortunately, research on the health-promoting properties of antioxidants has been ongoing. Subsequent years showed that the former assumption that all antioxidants acted similarly was greatly oversimplified. Redox-active compounds differ in their chemical structures, electrochemical properties, mechanisms of action, and bioavailability; therefore, their efficacy in protecting against oxidative stress also varies. In this review, we discuss the changing perception of oxidative stress and its sources, emphasizing everyday-life exposures, particularly those of dietary origin. Finally, we posit that a better understanding of the physicochemical properties and biological outcomes of antioxidants is crucial to fully utilize their beneficial impact on health.

Evolution of the Knowledge of Free Radicals and Other Oxidants

Free radicals are chemical species (atoms, molecules, or ions) containing one or more unpaired electrons in their external orbitals and generally display a remarkable reactivity. The evidence of their existence was obtained only at the beginning of the 20th century. Chemists gradually ascertained the involvement of free radicals in organic reactions and, in the middle of the 20th century, their production in biological systems. For several decades, free radicals were thought to cause exclusively damaging effects . This idea was mainly supported by the finding that oxygen free radicals readily react with all biological macromolecules inducing their oxidative modification and loss of function. Moreover, evidence was obtained that when, in the living organism, free radicals are not neutralized by systems of biochemical defences, many pathological conditions develop. However, after some time, it became clear that the living systems not only had adapted to the coexistence with free radicals but also developed methods to turn these toxic substances to their advantage by using them in critical physiological processes. Therefore, free radicals play a dual role in living systems: they are toxic by-products of aerobic metabolism, causing oxidative damage and tissue dysfunction, and serve as molecular signals activating beneficial stress responses. This discovery also changed the way we consider antioxidants. Their use is usually regarded as helpful to counteract the damaging effects of free radicals but sometimes is harmful as it can block adaptive responses induced by low levels of radicals.

Using oxidant susceptibility of thiol stabilized nanoparticles to develop an inflammation triggered drug release system

Ultrasmall thiol passivated ZnS NPs are prepared using a newly developed synthetic protocol. Exposure to hydroxyl radicals results in oxidation of the thiol groups, thus destabilizing the ZnS nanolids to open drug encompassing pores for attaining an inflammation responsive drug delivery system.

Hippocampal protection in mice with an attenuated inflammatory monocyte response to acute CNS picornavirus infection

Neuronal injury during acute viral infection of the brain is associated with the development of persistent cognitive deficits and seizures in humans. In C57BL/6 mice acutely infected with the Theiler's murine encephalomyelitis virus, hippocampal CA1 neurons are injured by a rapid innate immune response, resulting in profound memory deficits. In contrast, infected SJL and B6xSJL F1 hybrid mice exhibit essentially complete hippocampal and memory preservation. Analysis of brain-infiltrating leukocytes revealed that SJL mice mount a sharply attenuated inflammatory monocyte response as compared to B6 mice. Bone marrow transplantation experiments isolated the attenuation to the SJL immune system. Adoptive transfer of B6 inflammatory monocytes into acutely infected B6xSJL hosts converted these mice to a hippocampal damage phenotype and induced a cognitive deficit marked by failure to recognize a novel object. These findings show that inflammatory monocytes are the critical cellular mediator of hippocampal injury during acute picornavirus infection of the brain.

Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stress in men

OBJECTIVE

We examined the effects on serum sex steroids, lipids and markers of oxidative stress of supplementing the diets of healthy male volunteers with scones made with soya flour.

DESIGN

A randomized placebo controlled cross-over trial.

SETTING

University Hospital of Wales.

SUBJECTS

Twenty volunteers recruited by advertisement.

INTERVENTIONS

Male volunteers ate three scones a day in addition to their normal diet for a period of 6 weeks. The scones were made with either wheat or soya flour (containing 120 mg/day of isoflavones). Blood was analysed for sex steroids (testosterone, dihydro-testosterone, oestradiol, oestrone, sex hormone binding globulin, albumin and the concentration of non-protein bound sex steroids were calculated), lipid profile (total cholesterol, high density lipoprotein cholesterol and triglycerides) and measures of oxidative stress (hydroperoxides, susceptibility of LDL to oxidation with copper and myeloperoxidase).

RESULTS

The volunteers' mean age was 35.6 (s.d. 11.2) y. Total serum testosterone fell in volunteers taking the soya scones (19.3-18.2 nmol/l; 95% CI 1.01, 1.12; P=0.03). No significant changes were seen in the concentrations of the other serum sex steroids, albumin or sex hormone binding globulin throughout the study. Significant improvements in two of the three markers of oxidative stress were seen in volunteers taking soya scones. Lag time for myeloperoxidase rose from 55.0 to 68.0 min (95% CI -16.0, -3.5; P=0.009) and the presence of hydroperoxides decreased from 2.69 to 2.34 micro mol/l (95% CI 0.12, 0.71; P=0.009). There were no changes seen in serum triglycerides or cholesterol.

CONCLUSIONS

We have shown that soya supplements reduce serum testosterone and improve markers of oxidative stress. These findings provide a putative mechanism by which soya supplements could protect against prostatic disease and atherosclerosis. Further dietary studies with clinical end points are warranted.

Oxidative stress in phagocytes--"the enemy within"

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

C-terminal fragment of alpha1-antitrypsin activates human monocytes to a pro-inflammatory state through interactions with the CD36 scavenger receptor and LDL receptor

Monocyte scavenger receptor, CD36 has been implicated in the pathogenesis of atherosclerosis as a major oxidised LDL receptor mediating lipid accumulation and foam cell formation. Previously, we found that treatment of monocyte cultures with the carboxyl terminal fragment of alpha1-antitrypsin (C-36) increases lipid binding and uptake, induces LDL receptor mRNA and CD36 receptor protein expression, and also significantly increases production of pro-inflammatory molecules. To assess the role of the CD36 receptor in proatherogenic monocyte activation by the C-36 fragment, we tested whether specific anti-CD36 receptor antibodies would block the effects of C-36 on monocyte activation. We find that pre-incubation of cells with anti-LDL and anti-CD36 receptor antibodies (10 microg/ml) blocks binding of 125I-C-36 by about 50%. Similarly, cells pre-incubated with oxidised LDL or native LDL at concentrations from 2.5 to 10 microg/ml showed a loss of 125I-C-36 binding (up to 49 and 57%) and uptake (up to 47 and 59.8%), respectively. In parallel experiments, monocytes were first incubated for 1 or 6 h with anti-CD36 antibodies (10 microg/ml) prior to adding C-36 peptide. Anti-CD36 antibodies suppressed C-36-induced production of gelatinase B, monocyte chemoattractant protein-1, interleukin-6 and cellular oxygen consumption to control levels, whereas levels of TNFalpha were unaffected. In contrast, saturation of LDL receptors with excess of anti-LDL (20 microg/ml) significantly inhibited C-36 induced TNFalpha levels. Results indicate that the C-36 peptide binds to both LDL and CD36 scavenger receptors which involves selective upregulation of pro-inflammatory molecules and activation of the respiratory burst in human monocytes. This also supports important roles for CD36 and LDL receptors in atherogenesis and suggests that blockade of CD36 receptor can be protective in pro-inflammatory activation of human monocytes.

Effects of Noninhibitory α-1-Antitrypsin on Primary Human Monocyte Activation in Vitro

A major function of alpha-1-antitrypsin (AAT) is the inhibition of overexpressed serine proteinases during inflammation. However, it is also known that the biological activity of AAT is affected by chemical modifications, including oxidation of the reactive-site methionine, polymerization, and cleavage by unspecific proteases, all of which will result in AAT inactivation and/or degradation. All inactive forms of AAT can be detected in tissues and fluids recovered from inflammatory sites. To test for a possible link between the inflammation-generated, noninhibitory, cleaved form of AAT and cellular processes associated with inflammation, we studied the effects of this form at varying concentrations on human monocytes in culture. We found that cleaved AAT at concentrations ranging between 1 and 10 microM in monocyte cultures over 24 h induces elevation in monocyte chemoattractant protein-1 (MCP-1) and pro-inflammatory cytokines such as TNFalpha and IL-6 and also increases production of interstitial collagenase (MMP-1) and gelatinase B (MMP-9), members of two different classes of matrix metalloproteinase. Moreover, monocytes stimulated with higher doses of cleaved AAT show an increase in cellular oxygen consumption by about 30%, while native AAT under the same experimental conditions inhibits oxygen consumption by about 50%. These results indicate that the cleaved form of AAT may play a role in monocyte recruitment and pro-inflammatory activation during inflammatory processes, and also suggest that changes in structure occurring upon AAT cleavage could alter its functional properties with potential pathological consequences.

Atherogenic properties of human monocytes induced by the carboxyl terminal proteolytic fragment of alpha-1-antitrypsin

Atherosclerotic plaques contain a significant number of macrophage foam cells and are associated with an inflammatory state. Inflammation induces the secretion from monocytes and other cells of cytokines, reactive oxygen species, proteinases and proteinase inhibitors among many other molecular species. AAT is prominent among the serine proteinase inhibitors and is an important regulator of leukocyte elastase and proteinase-3. It has been shown that the stable AAT-proteinase complex can upregulate AAT biosynthesis, and we have shown that the shorter, carboxyl terminal peptide (C-36) resulting from proteinase cleavage of AAT polymerizes, and in its fibrillar form alters cellular metabolism. To test for a possible link between the inflammation-generated C-36 peptide and cellular processes associated with atherogenesis, we have studied the effects of the fibrillar form of this peptide at varying concentrations on human monocytes in culture. We have found that fibrillar C-36 at concentrations of greater than or equal to 5 micromol/l in monocyte cultures for 24 h significantly increases LDL binding and uptake, upregulates LDL receptors, induces cytokine production and glutathione reductase activity, and upregulates AAT synthesis. The expression of CD36 protein, LDL Scavenger receptor, is also upregulated by fibrillar C-36 and native LDL in the presence of C-36-activated monocytes is more oxidized than with unactivated control monocytes. The majority of monocytes cultured for 24 h in the presence of C-36 fibrils were transformed morphologically into macrophages. These data establish a direct molecular link, mediated by C-36 peptide of AAT, between inflammation and the oxidation and accumulation of lipid in monocyte-derived macrophages. This may be important for an understanding of the events conducive to atherogenesis.

Human monocyte activation by cleaved form of alpha-1-antitrypsin involvement of the phagocytic pathway

Production of alpha-1-antitrypsin (AAT) by human monocytes is an important factor in controlling tissue damage by proteases in the microenvironment of inflammation. Increases, of four- to eightfold, in numbers of macrophages and levels of AAT and its cleavage fragments have been found in various inflammatory loci. We have found that the C-terminal peptide (C-36) of AAT, produced by specific proteinase cleavage when added in its fibrillar form at concentrations >/=5 microM to monocytes in culture for 24 h, significantly increases low density lipoprotein (LDL) binding and uptake, up-regulates levels of LDL receptors and also induces proinflammatory cytokine (interleukin-1, interleukin-6 and tumour necrosis factor alpha) production and glutathione reductase activity. Because it is known that various cells selectively internalize surface receptors and their ligands through receptor-mediated endocytosis via clathrin-coated pits, we tested whether antibodies raised against the clathrin heavy chain would block the effects of the fibrillar form of C-36 on human monocytes in culture. Addition of excess anti-(clathrin HC) with 10 microM fibrillar C-36 diminished the stimulatory effects of the latter on LDL binding, uptake and LDL receptor levels. In contrast, however, in the presence of anti-(clathrin HC), the potentially cytotoxic effects of fibrils, such as induction of cytokines, free radicals and cytosolic activity of cathepsin D, were much greater than those observed when cells were treated with fibrils alone. These results suggest that endocytosis is the pathway by which C-36 fibrils upregulate LDL receptors, and may be the natural mechanism for fibril clearance. We infer that human monocytes clear C-36 fibrils by a clathrin-dependent pathway, presumably endocytotic, and that loss of this pathway amplifies the cytotoxic effects of the fibrils by increasing their availability to other specific or nonspecific sites through which they exert their cytotoxic effects.

High blood pressure, oxygen radicals and antioxidants: etiological relationships

This hypothesis proposes that high blood pressure is a pathological state associated with a loss of the balance between pro-oxidation and antioxidation, energy depletion, and accelerated aging in the target organs, such as heart, kidney and brain. Different nutritional, environmental, pharmacological factors and/or associated pathologies (diabetes, arteriosclerosis, cancer, alcoholism, etc.) and/or genetic components, can induce high blood pressure by breaking the redox equilibrium in the affected organs. Additional evidence, such as increase of oxidative damage, fibrogenesis, inhibition of the cardiocytic sodium-potassium pump, and heart hypertrophy, supports this hypothesis. These facts are analysed in the present paper, showing that they could contribute to the development of high blood pressure and associated pathologies by oxidative mechanisms.

Influence of polysaccharides on neutrophil function: specific antagonists suggest a model for cooperative saccharide-associated inhibition of immune complex-triggered superoxide production

We have previously shown that certain monosaccharides (N-acetyl-D-glucosamine and mannose) could cooperatively inhibit the ability of neutrophils to release superoxide anions in response to immune complexes. To test the possible origins of the cooperative inhibition of superoxide release, we have examined the effect of a panel of polysaccharides on superoxide release in the presence or absence of immune complexes. Although exposure to particulate beta-glucan and hyaluronan triggered superoxide release from neutrophils, other polysaccharides including chitin and mannan were without effect. Both chitin and mannan, but not other polysaccharides, inhibited the immune complex-mediated stimulation of superoxide release in a dose-dependent fashion. In sharp contrast to the cooperative inhibition mediated by monosaccharides, chitin and mannan exhibited Hill coefficients of 1. This inhibition of superoxide production was not due to simple blockage of Fc receptors since fluorescent immune complexes bound equally well to neutrophils in the presence or absence of mannan or chitin as shown by epifluorescence microscopy and quantitative fluorometry. Furthermore, this inhibition of superoxide release was not observed when neutrophils were stimulated with phorbol myristate acetate and ionophore A23187 or hyaluronan. Therefore, the specific inhibition of superoxide production by mannan and chitin could not be explained by either receptor blockage or by some nonspecific effect on cells. We suggest that these molecules interfere with a step in transmembrane signaling, presumably involving the integrin CR3. The observed Hill coefficients suggest the possibility that one polysaccharide may simultaneously bind to two monosaccharide binding sites yielding a Hill coefficient of 1, whereas individual monosaccharides separately bind yielding a Hill coefficient of 2.

The role of lactoferrin as an anti-inflammatory molecule

The formation of hydroxyl radical via the iron catalyzed Haber-Weiss reaction has been implicated in phagocyte-mediated microbicidal activity and inflammatory tissue injury. The fact that neutrophils contain lactoferrin and mononuclear phagocytes have the capacity to acquire exogenous iron has suggested that iron bound to lactoferrin may influence the nature of free radical products generated by these cells. Over the years the iron-lactoferrin complex has been heralded as both a promoter and inhibitor of hydroxyl radical formation. This manuscript is intended to provide an overview of work performed to date related to this controversy and to present results of a number of preliminary studies which shed further light on the role of lactoferrin in inflammation.

Superoxide-mediated lysis of erythrocytes: the role of colloid-osmotic forces

Although superoxide anions are a well-known mediator of cytotoxicity, their mechanism of target cell lysis is not clearly understood. In the present study we have used an exogenous source of superoxide to study erythrocyte cytolysis. RBC lysis was studied in buffers containing the cations Li+, Na+, K+, Rb+, and Cs+; superoxide anions were produced and available in these buffers. During this model superoxide-dependent cytolytic process, erythrocytes underwent a shape change from biconcave disk to sphere as shown by scanning electron microscopy. Soret band transmitted light microscopy has confirmed this shape change and shown that it precedes cytosolic oxidation. This evidence is consistent with a colloid-osmotic type lytic mechanism. Erythrocyte lysis was studied by 51Cr-release and light scattering methods. Superoxide-mediated target cytolysis was characterized by: 1) a sigmoidal dose-response curve and 2) a lag time in cytolysis after superoxide addition in kinetic light scattering experiments. The efficacy of cytolysis followed the rank order Cs+ > Rb+ > Na+, Li+ > sucrose = raffinose, which provides additional support for a colloid-osmotic lytic mechanism. Furthermore, the rank order potency correlates with the cations' hydration numbers. We suggest that oxidative events trigger the formation of colloid-osmotic pores approximately 1 nm in diameter.

Human intestinal mucosa alters T-cell reactivities

BACKGROUND

Compared with T cells in peripheral blood, lamina propria T lymphocytes have a low proliferative response to stimulation via the T-cell antigen receptor/CD3 complex or by protein kinase C activators yet largely preserve or even show an enhanced reactivity to CD2 and CD28 triggering. Coculture of peripheral blood T lymphocytes with intestinal mucosa supernatant leads to a similar functional behavior as found in freshly recovered lamina propria T lymphocytes. The aim of this study is to characterize the nature of substances in the mucosal supernatant responsible for downregulation of T-cell receptor-dependent signals.

METHODS

Mucosal supernatant was produced, dialyzed, digested with proteinase K, reduced by 2-mercaptoethanol or dithiothreitol, and tested for its activity on peripheral blood T lymphocytes.

RESULTS

Supernatant lost its activity after dialysis through a membrane (pore size 12,000-14,000). Digestion with proteinase K does not abolish its activity suggesting that the substances are neither proteins nor peptides. However, its effects on T lymphocyte proliferation can be reversed by reducing agents like 2-mercaptoethanol or dithiothreitol, suggesting that oxidative substances are contained in mucosal supernatants.

CONCLUSIONS

Our data support the view that mucosal substances that down-regulate antigen receptor-induced T lymphocyte proliferation are small, nonprotein, nonpeptide molecules with oxidative properties.

Simultaneous calcium-dependent delivery of neutrophil lactoferrin and reactive oxygen metabolites to erythrocyte targets: evidence supporting granule-dependent triggering of superoxide deposition

Optical microscopic techniques have been utilized to study the deposition of lactoferrin, a specific granule marker, and superoxide anions into target erythrocytes during antibody-dependent phagocytosis. Previous studies from this laboratory have shown that the entry of superoxide anions into erythrocytes can be sensitively monitored with Soret band transmitted light microscopy. When neutrophils were incubated with BAPTA/AM, an intracellular Ca2+ chelator, they phagocytosed IgG-opsonized sheep red blood cells (SRBC) but did not affect the microscopically detected absorption of their Soret band. When these same erythrocytes were observed after the infusion of 20 microM ionomycin, a Ca2+ ionophore, 58% of the cell-bound SRBC targets were destroyed immediately. However, neutrophils from chronic granulomatous disease (CGD) patients were unable to affect the Soret absorption of erythrocyte targets under any conditions. These results suggest that a Ca2+ signal can participate in triggering superoxide deposition in targets. Since Ca2+ signals are known to participate in the exocytic release of granules, we tested the hypothesis that specific lactoferrin-bearing granules are delivered to targets in parallel with superoxide anions. Lactoferrin delivery to phagosomes was monitored using resonance energy transfer (r.e.t.) microscopy. SRBCs were opsonized with both unconjugated and rhodamine B isothiocyanate (RBITC)-conjugated rabbit anti-SRBC IgG. After incubation with adherent neutrophils, the samples were washed, fixed with 3.7% paraformaldehyde, then labeled with fluorescein isothiocyanate (FITC)-conjugated antilactoferrin IgG. Energy transfer between FITC and RBITC was imaged microscopically and quantitated by photon counting. Significant levels of r.e.t. between antilactoferrin and anti-SRBC labels were observed after phagocytosis, but not in the absence of acceptor fluorochromes. To control for r.e.t. specificity, neutrophil membranes were labeled with FITC-conjugated, anti-HLA IgG after internalization of rhodamine B-tagged SRBCs (RSRBCs). Although r.e.t. between lactoferrin and RSRBCs labels was observed, no r.e.t. between HLA and RSRBC labels could be found. Further studies showed that treatment of neutrophils with BAPTA inhibited r.e.t. between anti-lactoferrin and RSRBCs. However, addition of ionomycin relieved this inhibition of energy transfer. These experiments show that both lactoferrin and superoxide delivery to targets are regulated in parallel by a Ca(2+)-dependent pathway. Furthermore, by combining Soret microscopy with r.e.t. microscopy, we have shown that superoxide anions and lactoferrin are delivered to the same phagosomes. We speculate that the NADPH oxidase, which produces superoxide anions, is assembled on specific granule membranes, thus accounting for their parallel Ca(2+)-dependence, activation, and delivery.

Iron sequestration by macrophages decreases the potential for extracellular hydroxyl radical formation

Alveolar macrophages (AM) from smokers contain a much higher quantity of intracellular iron than AM from nonsmokers. Since some forms of iron will catalyze the formation of hydroxyl radical (.OH) from superoxide and hydrogen peroxide, the ability of AM derived from smokers and nonsmokers to generate .OH was assessed. No detectable .OH was produced by AM from either source, suggesting that iron sequestration by AM may limit the potential for .OH-mediated lung injury. Consistent with this hypothesis, the ability of bronchoalveolar lavage fluid (BAL) from smokers and nonsmokers to act as an .OH catalyst decreased after exposure to AM. We found that, like AM, human monocyte-derived macrophages (MDM) have the ability to acquire large quantities of iron from small low molecular weight iron chelates as well as decrease the ability of BAL to act as a .OH catalyst. When MDM or AM were exposed to the iron chelates or BAL they were then able to generate .OH after phorbol myristate acetate stimulation. However, when acutely iron-loaded or BAL-exposed MDM were placed in culture, their ability to produce .OH decreased with time to the level of non-iron-exposed controls. This process correlated with iron translocation from the plasma membrane to the cytosol as well as a 3-9-fold increase in cellular ferritin. No increase in antioxidant enzyme levels or induction of the heat shock response was observed. Iron sequestration by macrophages may protect nearby cells from exposure to potentially cytotoxic iron-catalyzed oxidants such as .OH.

Imaging neutrophil activation: analysis of the translocation and utilization of NAD(P)H-associated autofluorescence during antibody-dependent target oxidation

Fluorescence intensified/enhanced microscopy has been used to study the metabolic activation of living human neutrophils in time-lapse sequences. The autofluorescence associated with NAD(P)H's emission band was studied within individual quiescent and stimulated cells. Excitation of NAD(P)H-associated autofluorescence was provided by a high-intensity Hg-vapor lamp. The background-subtracted autofluorescence signals were computer enhanced. In some cases the ratio image of NAD(P)H-associated autofluorescence to tetramethyl-rhodamine methyl ester (TRME) fluorescence, which was found to be uniformly distributed within neutrophils, was calculated to normalize autofluorescence intensities for cell thickness. Activation of the NADPH oxidase by phorbol myristate acetate, F-, N-formyl-methionyl-leucyl-phenylalanine (FMLP), or tumor necrosis factor (TNF) dramatically reduced autofluorescence levels. Membrane solubilization with sodium dodecyl sulfate eliminated autofluorescence. Thus, control experiments indicated that most or all of the detectable NAD(P)H-associated autofluorescence was due to NAD(P)H, consistent with previous non-microscopic studies. To understand the metabolic events surrounding the internalization and oxidative destruction of targets, we have imaged the NAD(P)H-associated autofluorescence of neutrophils and the Soret band of antibody coated target erythrocytes during cell-mediated cytotoxicity. Absorption contrast microscopy of the erythrocyte's Soret band is an especially sensitive indicator of the entry of reactive oxygen metabolites into this target's cytosol. Thus, it is possible to spectroscopically dissect and image the substrate (NADPH) and product (O2-) reactions of the NADPH oxidase in living unlabeled neutrophils. During real-time experiments at 37 degrees C, the level of NAD(P)H-associated autofluorescence surrounding phagosomes greatly increases before the disappearance of the target's Soret band. NAD(P)H-associated autofluorescence in the vicinity of phagocytosed erythrocytes is greatly diminished after target oxidation. This suggests that NAD(P)H is translocated to the vicinity of phagosomes prior to the oxidation of targets. The apparent cytosolic redistribution of NAD(P)H was confirmed by ratio imaging microscopy to control for cell thickness. We suggest that NADPH including its sources and/or carriers accumulate near phagosomes prior to target oxidation and that local NADPH molecules are consumed during target oxidation.

Generation of superoxide anion and candidacidal activity by lipopolysaccharide-treated macrophages from patients affected by neoplasia

Macrophages, derived from in vitro cultured monocytes from both healthy donors and patients affected by metastatic breast cancer, treated or not with Escherichia coli lipopolysaccharide (LPS), were tested for phagocytosis and intracellular killing of Candida albicans and superoxide anion release. We found a marked impairment in intracellular killing closely linked to the lack of superoxide production in macrophages from patients affected by neoplasia treated or not with LPS. On the other hand, the LPS treatment significantly enhanced the phagocytic activity of all the macrophage populations tested, except for phagocytes obtained from patients affected by neoplasia and differentiated in autologous serum.

Kinetics of superoxide production by stimulated neutrophils

Oxygen-derived active species and superoxide radical in particular are generated and excreted upon granulocyte activation and are instrumental in host defense against bacterial and fungal infections. Associated with the activation of neutrophils is an apparent transitory oxy-radical production. Evidence from independent methods has previously suggested that radical production peaks shortly following neutrophil stimulation and decays within minutes. However, since neutrophil function in the body might reasonably be expected to last beyond the few minutes following stimulation, cessation of the production of oxy-radicals is unexpected. In an attempt to reconcile this discrepancy, the formation kinetics of superoxide by stimulated human neutrophils was reinvestigated by three independent methods: electron spin resonance, chemiluminescence, and ferricytochrome c reduction. The present results demonstrate that under appropriate experimental conditions stimulated neutrophils have the capacity to produce superoxide for several hours. The reasons for the previously reported "apparent" ephemeral nature of oxy-radical formation are discussed.

Superoxide production by stimulated neutrophils: temperature effect

Activation of neutrophils results in a one-electron reduction of oxygen to produce the superoxide anion and other oxygen-derived, microbicidal species. Evidence from many kinetic studies of oxygen-derived radicals generated by stimulated neutrophils in vitro shows that radical production is optimal at 37 degrees C but only lasts several minutes and then rapidly subsides. These findings support the widely held perception that the neutrophil's "oxidative burst" is a transitory event that peaks within minutes of stimulation and ends shortly thereafter. However, while some studies have shown that under controlled conditions stimulated neutrophils can generate superoxide continuously for several hours, others have observed that the superoxide formation by neutrophils stimulated in buffer at 37 degrees C does not persist. To reconcile the conflicting findings and to better understand neutrophil function, we have reinvestigated the effect of temperature on the kinetics of radical generation by PMA-stimulated cells. Electron paramagnetic resonance spectroscopy coupled with spin-trapping and SOD-inhibitable ferricytochrome c reduction were used to monitor superoxide production by neutrophils stimulated at either 25 degrees C or 37 degrees C in RPMI 1640 medium or in Hank's balanced salt solution. When oxygen was supplied continuously, neutrophils stimulated at 25 degrees C in buffer or in medium generated superoxide for several hours but at 37 degrees C, particularly in HBSS, O2- formation strikingly and rapidly decreased. This cessation of superoxide generation was reversible by lowering the temperature back to 25 degrees C. These data imply that in vivo neutrophils may be capable of generating oxy-radicals for prolonged periods. In part, our results may also explain the often observed termination of neutrophil-derived radical formation in vitro and help to dispel the perception that neutrophil-derived oxy-radical production is an ephemeral phenomenon.

Inhibitory effect of eugenol on Cu2+-catalyzed lipid peroxidation in human erythrocyte membranes

1. The effects of eugenol on lipid peroxidation catalyzed by hydrogen peroxide (H2O2) or benzoyl peroxide (BPO) in the presence of copper ions were studied in human erythrocyte membranes. 2. The production of hydroxyl radicals was suggested in the peroxidation system catalyzed by H2O2/Cu2+. 3. H2O2/Cu2+-dependent peroxidation was inhibited by eugenol in a concentration-dependent manner; peroxidation was inhibited 62% by 200 microM eugenol. 4. In the presence of eugenol, the peroxidation catalyzed by BPO/Cu2+ was inhibited in a concentration-dependent manner, and more than 100 microM eugenol completely inhibited peroxidation. 5. The inhibitory effect of eugenol was non-competitive against Cu2+ in H2O2/Cu2+- and BPO/Cu2+-dependent peroxidation. 6. It is suggested that eugenol inhibits formation of hydroxyl radicals.

Mononuclear phagocytes have the potential for sustained hydroxyl radical production. Use of spin-trapping techniques to investigate mononuclear phagocyte free radical production

Monocytes lack lactoferrin and have much less myeloperoxidase than neutrophils. They also acquire a potential catalyst for .OH production (tartrate-resistant acid phosphatase) as they differentiate into macrophages. Consequently, the nature of free radicals produced by these cells was examined using the previously developed spin-trapping system. When stimulated with either PMA or OZ neither monocytes nor monocyte-derived macrophages (MDM) exhibited spin trap evidence of .OH formation. Pretreatment with IFN-gamma failed to induce MDM .OH production. When provided with an exogenous Fe+3 catalyst, both stimulated monocytes and MDM, but not PMN, exhibited sustained .OH production, presumably due to the absence of lactoferrin in mononuclear phagocytes. Sustained production of .OH could contribute to the microbicidal activity of mononuclear phagocytes as well as inflammatory tissue damage under in vivo conditions where catalytic Fe+3 may be present.

Trypanosoma brucei: susceptibility to hydrogen peroxide and related products of activated macrophages

The susceptibility of procyclic, trypsinized, or bloodstream forms of Trypanosoma brucei to lysis by hydrogen peroxide and by activated mouse macrophages was investigated in vitro using the release of biosynthetically labeled proteins as an assay. Uncoated parasites were more resistant than coated bloodstream forms in both cases. Macrophage trypanolysis upon triggering with phorbol myristate acetate occurred extracellularly and seemed to depend on the release of hydrogen peroxide, as it was prevented by catalase. However, when presented trypanosomes in presence of fresh immune serum which was itself lytic, macrophages did not show any additional lytic effect, and phagocytosis was related to already damaged parasites.

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.

Evaluation and improvements of a rapid microassay for measuring superoxide anion production by phagocytes. 2. Biochemical aspects

Superoxide anion synthesis by stimulated human polymorphonuclear leukocytes (PMNL) may be measured as superoxide dismutase-inhibitable cytochrome C (Cytc) reduction in a rapid microplate assay. However, when determinations are made over a fixed time interval (15 min) a lack of proportionality is observed between the amount of Cytc reduced and the number of cells stimulated. Examination of the reduction kinetics indicated that depressed superoxide detection at higher cell densities might be a consequence of Cytc re-oxidation by later metabolites in the oxidative burst. This was confirmed using dithionite-reduced Cytc as substrate in the assay. A method of analysis which avoids this source of error in determining superoxide anion synthesis is proposed.

Neutrophil-mediated cytotoxicity triggered by immune complexes: the role of reactive oxygen metabolites

Normal human neutrophils triggered by precipitating immune complexes (IC), soluble IC (sIC) or heat-aggregated IgG (HAIgG) displayed low levels of cytotoxicity towards nonsensitized target cells. Catalase, but not heated catalase, completely impaired this nonspecific cytotoxicity (NSC), suggesting a key role for hydrogen peroxide (H2O2) in the lysis of target cells. Superoxide dismutase (SOD) and certain HO. and 1O2 scavengers were unable to exert significant effects. Three haem-enzyme inhibitors, sodium azide, sodium cyanide and 3-amino-1,2,4-triazole did not decrease neutrophil NSC, but markedly enhanced it. This data suggest that the mechanism involved was not dependent upon myeloperoxidase (MPO). The analysis of neutrophil-mediated ADCC indicates that oxygen-dependent but MPO-independent mechanisms appeared to be operative in this system. It was also found that the microfilament disrupting agents, cytochalasin B (CB) and dihydrocytochalasin B (dhCB), as well as the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP), significantly enhanced NSC. In contrast, these compounds partially inhibited ADCC. This cytotoxic system provides a suitable model to study events that may occur during the course of immune complex diseases and also permits the evaluation of alternative lytic mechanisms triggered through neutrophil Fc gamma receptors.

The role of reactive oxygen intermediates in nonspecific monocyte cytotoxicity induced by immune complexes

Normal human monocytes were induced to lyse nonsensitized target cells when triggered by precipitating immune complexes (IC) or soluble heat-aggregated IgG (HAIgG). Catalase, azide, cyanide and three aminoacids employed as quenchers of ClO, significantly inhibited this nonspecific cytotoxicity (NSC), suggesting an important role for the myeloperoxidase (MPO) system. However, HO and/or 1O2 may also be involved in the lysis, since certain scavengers of these species such as mannitol, benzoate, ethanol and histidine, as well as superoxide dismutase (SOD), partially inhibited NSC. Moreover, cyanide and azide were unable to completely abrogate this lytic activity. When NSC was compared to antibody dependent cellular cytotoxicity (ADCC), it was found that neither catalase nor oxygen-species scavengers affected ADCC while azide and cyanide significantly enhanced it. Antibody-coated target cells were also destroyed by IC-triggered monocytes. However, kinetic analysis and studies on the capacity of catalase to inhibit the lysis demonstrated that it was mediated through a NSC-like mechanism. The cytotoxic system described in this report offers a suitable model to study in vitro alternative lytic mechanisms triggered through monocyte receptors for the Fc portion of IgG (Fc gamma R).

Modulation of phagocytic cell function

Phagocytosis is an important factor in the defense of the host against all kinds of microorganisms. The process of phagocytosis of microorganisms by phagocytes can be separated into distinct but interrelated phases: adherence, chemotaxis, opsonization, attachment, ingestion, degranulation and killing. Phagocytosis is accompanied by an increase in oxygen metabolism in which H2O2 and activated oxygen species are generated. Modulation of phagocytic cell function can be brought about by a variety of substances. Microorganisms produce and contain components which influence the process of phagocytosis. Surrounding tissue cells and the phagocytes themselves produce biologically active molecules that modulate phagocytosis.

Complex-formation and reduction of ferric iron by 2-oxo-4-thiomethylbutyric acid, and the production of hydroxyl radicals

2-Oxo-4-thiomethylbutyric acid (OMBA) is a widely used oxygen-radical-scavenging agent and has been used for the detection of .OH-like species in a variety of systems. This scavenger reacts with other radicals and is therefore not specific for .OH. Since iron is required in most systems for the generation of OH-like species, studies were carried out to investigate the possible interaction of OMBA with iron. Fe3+ reacted with OMBA to produce complexes that gave rise to discrete spectra. Intense purple complexes, with broad absorbance maxima of 525-550 nm, were found at OMBA/Fe3+ ratios of up to 1:1, whereas red complexes with a prominent shoulder between 440 and 480 nm were found at higher OMBA/Fe3+ ratios. OMBA caused reduction of ferric iron to the ferrous state, as detected with 2,2'-bipyridyl as the indicator. This reduction occurs in the dark, can be photo-accelerated especially by light with wavelengths near the absorbance maximum of the respective complexes, and is increased as the OMBA/Fe3+ ratio is elevated. The presence of phosphate buffer quenches the purple and red ferric-ion-OMBA complexes and lowers the rate of reduction of Fe3+ by OMBA about 10-fold. The resulting ferrous-ion-OMBA-phosphate complex is very stable against autoxidation. Both the ferrous-ion-OMBA and ferric-ion-OMBA complexes reacted with H2O2, with the subsequent production of ethylene gas from OMBA. The interaction with H2O2 resulted in discrete spectral changes of both the ferrous-ion-OMBA and ferric-ion-OMBA complexes. The ferrous-ion-OMBA/H2O2 or ferric-ion-OMBA/H2O2 system appeared to produce .OH free radicals via a Fenton-type of reaction since ethylene production was inhibited by competitive OH scavengers. Ferrous-ion-OMBA complex reacted with H2O2 not only to produce ethylene from the OMBA, but also to promote the oxidation of another scavenger, ethanol. The ability of OMBA to chelate iron, to promote reduction of ferric iron and to react with H2O2 to produce potent oxidizing radicals may play a role in the lack of specificity of OMBA as a scavenger of oxygen radicals.

Metal ions and oxygen radical reactions in human inflammatory joint disease

Activated phagocytic cells produce superoxide (O2-) and hydrogen peroxide (H2O2); their production is important in bacterial killing by neutrophils and has been implicated in tissue damage by activated phagocytes. H2O2 and O2- are poorly reactive in aqueous solution and their damaging actions may be related to formation of more reactive species from them. One such species is hydroxyl radical (OH.), formed from H2O2 in the presence of iron- or copper-ion catalysts. A major determinant of the cytotoxicity of O2- and H2O2 is thus the availability and location of metal-ion catalysts of OH. formation. Hydroxyl radical is an initiator of lipid peroxidation. Iron promoters of OH. production present in vivo include ferritin, and loosely bound iron complexes detectable by the 'bleomycin assay'. The chelating agent Desferal (desferrioxamine B methanesulphonate) prevents iron-dependent formation of OH. and protects against phagocyte-dependent tissue injury in several animal models of human disease. The use of Desferal for human treatment should be approached with caution, because preliminary results upon human rheumatoid patients have revealed side effects. It is proposed that OH. radical is a major damaging agent in the inflamed rheumatoid joint and that its formation is facilitated by the release of iron from transferrin, which can be achieved at the low pH present in the micro-environment created by adherent activated phagocytic cells. It is further proposed that one function of lactoferrin is to protect against iron-dependent radical reactions rather than to act as a catalyst of OH. production.

In vivo production of ethylene from 2-keto-4-methylthiobutyrate in mice

The use of 2-keto-4-methylthiobutyric acid (KMB), the alpha-keto analog of methionine, was studied as a potential means of detecting free radical generation in vivo. KMB-dependent ethylene production (presumably from free radical interception), and ethane production from in vivo lipid peroxidation, were monitored simultaneously by measuring the rate of exhalation of these hydrocarbons by mice. Injection of KMB (1 g/kg) into mice resulted in an 8-fold increase in ethylene production above endogenous levels seen in saline-injected controls (1.47 +/- 0.35 vs 0.17 +/- 0.02 nmoles/100 g/hr respectively). Administration of CCl4 (3.0 g/kg) to initiate hepatic lipid peroxidation, 20 min prior to KMB injection, augmented the production of ethylene (2.37 +/- 0.10 nmoles/100 g/hr). Lipid peroxidation following injection of CCl4 was monitored via the increased exhalation of ethane. Pretreating the mice with vitamin E (100 mg/kg daily for 3 days), an inhibitor of lipid peroxidation, did not result in a significant change in ethylene production from KMB by itself or after prior injection of CCl4. However, vitamin E did suppress ethane production initiated by CCl4. Similar results were obtained with mouse liver slices studied in vitro. Metyrapone (150 mg/kg), an inhibitor of hepatic mixed function oxidase activity, also suppressed significantly the CCl4-stimulated production of ethane, but not the CCl4-stimulated production of ethylene from KMB. It appears that ethylene production from KMB does not derive from free radicals generated during in vivo lipid peroxidation since suppression of lipid peroxidation by vitamin E or metyrapone did not suppress ethylene production.

[DMNH chemiluminescence of ingesting monocytes]

We have described a method to measure the chemiluminescence of stimulated monocytes, which necessitated only a few ml blood and thus make possible the investigation of clinical problems. The measurement of the chemiluminescence of monocytes is performed in a suspension of mononuclear leukocytes containing 40%-50% monocytes and 50%-60% lymphocytes. The preparation of this suspension requires a smaller blood volume than that of a suspension of pure monocytes. This method is possible because of the incapability of lymphocytes to produce chemiluminescence. A further important element of the described procedure is the fact that contamination of the mononuclear cell suspension with polymorphonuclear leukocytes, which show pronounced activity of oxidative metabolism and thus a high degree of chemiluminescence, is excluded. The application of 7 Dimethylamino-naphthalene-1,2-dicarbonic acid hydrazide (DMNH) as highly efficient chemiluminescent oxidant indicator and of the sensitive chemiluminescence measuring instrument Biolumat LB 9 500 permit the assessment of the chemiluminescence activity of monocytes in 10(5) cells. By varying the single components of the measuring approach (number of monocytes, number of ingesting particles, concentration of DMNH) the testing conditions were examined and a standard approach was determined. The average value of the chemiluminescence of phagocytosing monocytes in healthy adults during 30 min measuring time is 3.13 (S = 0.79) X 10(6) relative light units/10(5) cells. The point of maximum photone emission per unit in time is reached after 5-10 min.

Effect of lipopolysaccharides, lipid A and interferon on the cell-mediated cytotoxicity of human leukocytes against K-562 tumor cells

The effect of lipopolysaccharides (LPS), lipid A and interferon on cell-mediated cytotoxicity was investigated using 51Cr-labeled K-562 tumor cells as targets. As effectors, peripheral blood mononuclear cells from healthy blood donors were obtained by Ficoll gradient centrifugation: mononuclear phagocytes were eliminated by iron phagocytosis and plastic adherence. A T cell-enriched population was obtained by passing mononuclear phagocyte-depleted mononuclear cells through nylon wool columns. LPS and lipid A augmented cell-mediated cytotoxicity provided mononuclear phagocytes were present. Supernatants from LPS-treated mononuclear phagocytes and T cells enhanced mononuclear phagocyte-mediated cytotoxicity to a higher degree than LPS and lipid A alone. This finding suggests the participation of a lymphokine. In contrast, the interferon preparation increased the cell-mediated cytotoxicity both of mononuclear phagocyte-containing and of mononuclear phagocyte-depleted effectors. Here, the participation of natural killer cells as effectors is suggested.

Ultrastructural localization of NADPH-oxidase activity in murine peritoneal macrophages during phagocytosis of Brucella. Correlation with the production of superoxide anions

The localization of the enzyme NADPH oxidase in mouse peritoneal macrophages unstimulated or after phagocytosis of Brucella suis was investigated by electron microscopy in normal mice and mice immunized against B. suis. The enzyme was clearly visualized on mitochondrial cristae, smooth endoplasmic reticulum, and the plasma membrane; its activity correlated mainly with the state of the endoplasmic reticulum which itself reflected macrophage activation. The enzyme turnover appeared to be accelerated after phagocytosis; the phagosome membrane was seldom stained by the enzyme reaction. These macrophages were also examined for the production of superoxide anions in vitro, either unstimulated or after phagocytosis. Phagocytosis increased the production of superoxide anions, especially in immunized animals. These results are discussed with regard to the role that the products of oxidative metabolism play in the inactivation of bacteria by phagocytic cells.