Chemiluminescence and superoxide generation by leukocytes stimulated by polyelectrolyte-opsonized bacteria. Role of histones, polyarginine, polylysine, polyhistidine, cytochalasins, and inflammatory exudates as modulators of oxygen burst

Effect of poly-L-arginine in inhibiting scrapie prion protein of cultured cells

Biological effect of poly-L-arginine (PLR), the linear homopolymer comprised of L-arginine, was investigated to determine the activity of suppressing prions. PLR decreased the level of scrapie prion protein (PrP^Sc) in cultured cells permanently infected with prions in a concentration-dependent manner. The PrP^Sc inhibition efficacy of PLR was greater than that of another prion-suppressant poly-L-lysine (PLK) in a molecular mass-dependent fashion. The effective concentration of PLR to inhibit prions was achieved safely below the cytotoxic concentrations, and overall cytotoxicity of PLR was similar to that of PLK. PLR did not alter the cellular prion protein (PrP^C) level and was unable to change the states of preformed recombinant PrP aggregates and PrP^Sc from prion-infected cells. These data eliminate the possibility that the action mechanism of PLR is through removal of PrP^C and pre-existing PrP^Sc. However, PLR formed complexes with plasminogen that stimulates prion propagation via conversion of PrP^C to the misfolded isoform, PrP^Sc. The plasminogen-PLR complex demonstrated the greater positive surface charge values than the similar complex with PLK, raising the possibility that PLR interferes with the role of cofactor for PrP^Sc generation better than PLK.

PADMA-28, a traditional tibetan herbal preparation inhibits the respiratory burst in human neutrophils, the killing of epithelial cells by mixtures of oxidants and pro-inflammatory agonists and peroxidation of lipids

Both aqueous and methanolic fractions derived from the Tibetan preparation PADMA-28 (a mixture of 22 plants) used as an anti-atherosclerotic agent, and which is non-cytolytic to a variety of mammalian cells, were found to strongly inhibit (1) the killing of epithelial cells in culture induced by 'cocktails' comprising oxidants, membrane perforating agents and proteinases; (2) the generation of luminol-dependent chemiluminescence in human neutrophils stimulated by opsonized bacteria; (3) the peroxidation of intralipid (a preparation rich in phopholipids) induced in the presence of copper; and (4) the activity of neutrophil elastase. It is proposed that PADMA-28 might prove beneficial for the prevention of cell damage induced by synergism among pro-inflammatory agonists which is central in the initiation of tissue destruction in inflammatory and infectious conditions.

Antimicrobial peptides and endotoxin inhibit cytokine and nitric oxide release but amplify respiratory burst response in human and murine macrophages

Antimicrobial peptides (AMPs), in addition to their antibacterial properties, are also chemotactic and signalling molecules that connect the innate and adaptive immune responses. The role of AMP [alpha defensins, LL-37, a cathepsin G-derived peptide (CG117-136), protegrins (PG-1), polymyxin B (PMX) and LLP1] in modulating the respiratory burst response in human and murine macrophages in the presence of bacterial endotoxin [lipopolysaccharide (LPS) or lipooligosaccharide (LOS)] was investigated. AMP were found to neutralize endotoxin induction of nitric oxide and TNFalpha release in macrophages in a dose-dependent manner. In contrast, macrophages primed overnight with AMP and LOS or LPS significantly enhanced reactive oxygen species (ROS) release compared with cells primed with endotoxin or AMP alone, while no responses were seen in unprimed cells. This enhanced ROS release by macrophages was seen in all cell lines including those obtained from C3H/HeJ (TLR4-/-) mice. Similar effects were also seen when AMP and endotoxin were added directly with zymosan to trigger phagocytosis and the respiratory burst in unprimed RAW 264.7 and C3H/HeJ macrophages. Amplification of ROS release was also demonstrated in a cell-free system of xanthine and xanthine oxidase. Although AMP inhibited cytokine and nitric oxide induction by endotoxin in a TLR4-dependent manner, AMP and endotoxin amplified ROS release in a TLR4-independent manner possibly by exerting a prolonged catalytic effect on the ROS generating enzymes such as the NADPH-oxidase complex.

Noninvasive in vivo evaluation of skin antioxidant activity and oxidation status

The method described here allows noninvasive quantification of reducing LMWA or the lipid hydroperoxide present on the surface of the skin. Quantification of reducing antioxidants can be achieved because they are secreted from the skin surface into a well containing an extraction solution. Analysis of the reducing equivalents released indicates the presence of uric acid and ascorbic acid. Other LMWA released from the skin are as yet unidentified. The secretion of the LMWA reaches a plateau following 20-30 min of incubation. Therefore, a 30-min incubation period was chosen as the optimal time for the extraction solution to be present in the well and in contact with the skin. This extraction procedure can be repeated after 24 hr. This period of time is needed for regeneration of the LMWA to their initial levels. Direct measurement allows continuous determination of the release of LMWA and their interaction with the iron chelate. The reaction is completed after 25-35 min, at which time the final potential can be recorded. When organic peroxides on the surface of the skin are determined, it is important that the glassy carbon electrode be in close contact with the skin, since the reaction occurs on the surface of the electrode and the bound peroxide on the outer layer of the skin. Furthermore, close contact is needed to avoid interference of reducing equivalents secreted from the skin into the well.

Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS)

Silicones (polydimethylsiloxane, PDMS) are the materials currently used in most breast implants. ICP and FTIR analysis of the tissue capsule around aged breast implants and in vitro models show that Si-containing material is leaking from the PDMS implants. In this study, the hydrolysis of PDMS has been theoretically modeled using a semiempirical quantum mechanical method called AM1. The activation barrier for removing a methanol monomer was found to be +82 Kcal/mol while the removal of a methane monomer was +41 Kcal/mol. Using the same AM1 method, hydrolysis of the identical to Si-O-Si identical to bond also has been modeled for pentasilicic acid and, in this study, for 1,1,3,3,-fetramethyldisiloxane-1,3-diol. The barrier to the removal of a silicon-containing tetrahedron for both studies was found to be +27 Kcal/mol. This is approximately one and a half times smaller than the energy of that needed to remove a methyl group. The pentacoordinated silicon-activated transition state for hydrolysis of PDMS may provide an energetically favorable pathway for development of a surface that will enhance chemisorption of charged protein molecules, and such a pathway may show up in NMR studies of the hydrolysis of PDMS.

Osteoclast radicals

In biological research, new ideas arise and quickly spread to encompass the entire field. Thus, the evolution of molecular biology has significantly changed our methods of approaching our research. A similar far-reaching finding has been the advent of radical reactions into biology. Although radical chemistry has been utilized for many technological advances that affect our daily lives, the appreciation of this same process within our cells has opened an unexplored arena for research enquiry. As cellular messengers, radical molecules seem whimsically designed: they are evanescent, rapidly and apparently indiscriminately reactive, and barely detectable by most biological methods. Yet, our initial probing of these reactive agents in cells and organisms has led us to postulate a virtually undescribed system of communication within and among cells which may have significant effects in multiple organs. In bone, radical reactants have been attributed with an important role in the control of bone resorption.

Chemiluminescence in activated human neutrophils: role of buffers and scavengers

Human neutrophils (PMNs) suspended in Hanks' balanced salt solution (HBSS), which are stimulated either by polycation-opsonized streptococci or by phorbol myristate acetate (PMA), generate nonamplified (CL), luminol-dependent (LDCL), and lucigenin-dependent chemiluminescence (LUCDCL). Treatment of activated PMNs with azide yielded a very intense CL response, but only a small LDCL or LUCDCL responses, when horse radish peroxidase (HRP) was added. Both CL and LDCL depend on the generation of superoxide and on myeloperoxidase (MPO). Treatment of PMNs with azide followed either by dimethylthiourea (DMTU), deferoxamine, EDTA, or detapac generated very little CL upon addition of HRP, suggesting that CL is the result of the interaction among H2O2, a peroxidase, and trace metals. In a cell-free system practically no CL was generated when H2O2 was mixed with HRP in distilled water (DW). On the other hand significant CL was generated when either HBSS or RPMI media was employed. In both cases CL was markedly depressed either by deferoxamine or by EDTA, suggesting that these media might be contaminated by trace metals, which catalyzed a Fenton-driven reaction. Both HEPES and Tris buffers, when added to DW, failed to support significant HRP-induced CL. Nitrilotriacetate (NTA) chelates of Mn2+, Fe2+, Cu2+, and Co2+ very markedly enhanced CL induced by mixtures of H2O2 and HRP when distilled water was the supporting medium. Both HEPES and Tris buffer when added to DW strongly quenced NTA-metal-catalyzed CL. None of the NTA-metal chelates could boost CL generation by activated PMNs, because the salts in HBSS and RPMI interfered with the activity of the added metals. CL and LDCL of activated PMNs was enhanced by aminotriazole, but strongly inhibited by diphenylene iodonium (an inhibitor of NADPH oxidase) by azide, sodium cyanide (CN), cimetidine, histidine, benzoate, DMTU and moderately by superoxide dismutase (SOD) and by deferoxamine LUCDCL was markedly inhibited only by SOD but was boosted by CN. Taken together, it is suggested that CL generated by stimulated PMNs might be the result of the interactions among, NADPH oxidase, (inhibitable by diphenylene iodonium), MPO (inhibitable by sodium azide), H2O2 probably of intracellular origin (inhibitable by DMTU but not by catalase), and trace metals that contaminate salt solutions. The nature of the salt solutions employed to measure CL in activated PMNs is critical.

Superoxide production during refeeding in patients with anorexia nervosa

The effect of undernutrition and refeeding on superoxide production by polymorphonuclear cells (PMN) was studied in 11 girls suffering from anorexia nervosa (AN) and 17 age-matched, normal, healthy, control subjects. Superoxide anion production by PMNs from undernourished AN patients was comparable to normal, while a significant decrease in this function was observed during the initial period of refeeding. After a more extended period of refeeding, superoxide production by PMNs from AN patients increased and gradually returned toward normal values. Superoxide production correlated with length of the refeeding period (RF), weight as a percentage of ideal weight for height (W/H%), and rate of weight gain (WG). These results imply that a variety of physiological parameters, including susceptibility to infection, may be altered by refeeding undernourished patients.

Augmentation of the antibacterial activity of magainin by positive-charge chain extension

Novel analogs of the broad-spectrum antimicrobial peptide magainin-2 were obtained by extension of its chain through addition of segments of positively charged amino acids to either its N or its C terminus and by increasing its helicity. The activity of magainin-2 toward American Type Culture Collection strains of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus was most considerably enhanced by these modifications, whereas, in general, its low hemolytic capacity was not or was only slightly affected. The antibacterial potencies of magainin-2 and its derivatives were more evident following decreases of pH from 7.2 to 6 and 5.

Changes of plasma membrane permeability in neutrophils treated with polycations

The effects of the polycations poly-L-arginine, poly-L-lysine, and poly-ethyleneimine on rabbit neutrophil membrane permeability were compared. LDH release, quin2 release from quin2-loaded cells, and increase of indo 1 fluorescence were considered as measures for changes in membrane permeability. All polycations cause abundant LDH release. Quin2 release occurs more rapidly than LDH release, and the increase of indo 1 fluorescence is even faster. Apparently polycation-induced permeability changes occur gradually, allowing the influx (or efflux) of small molecules more rapidly than larger ones. A number of divalent and trivalent cations inhibit polycation-induced LDH and quin2 release in a way that resembles the inhibition of other cytotoxic agents described in literature. In the absence of extracellular Ca2+, the polycations induce little lysozyme release. In the presence of extracellular Ca2+, there is abundant lysozyme release, indicating that the influx of Ca2+ causes exocytosis. Exocytosis still occurs when Ca2+ is added some time after polycation addition, indicating that polycation treatment leaves the cells largely intact. All polycations tested have in common that they cause gradual changes in the permeability of the plasma membrane only, which opens the possibility to use them as membrane-permeabilizing agents for the study of Ca(2+)-induced exocytosis.

Superoxide formation and chemiluminescence of peripheral polymorphonuclear leukocytes in rapidly progressive periodontitis patients

Previous studies have indicated that in certain types of chronic inflammatory periodontal diseases, polymorphonuclear leucocytes (PMN) functions are impaired. In view of the damage oxygen free radicals may cause to the periodontal tissues, the present study focussed on superoxide (SO) formation and luminol-dependent chemiluminescence (LDCL) by peripheral PMN cells in rapidly progressive periodontitis patients (RPP). PMN cell preparations were stimulated by either opsonized bacteria or phorbol myristate acetate (PMA). The results indicate that PMN cells from RPP patients, stimulated by opsonized bacteria, have significantly enhanced SO formation and LDCL response as compared to healthy subjects. The hyperactivity was cell-associated. In the presence of PMA, no significant differences were detected between the groups. The results suggest that PMN cells from RPP patients are functionally activated, and produce elevated levels of oxygen radicals. These oxygen radicals may play a role in the pathogenesis of RPP.

The SOD like activity of copper:carnosine, copper:anserine and copper:homocarnosine complexes

Carnosine, anserine and homocarnosine are natural compounds which are present in high concentrations (2-20 mM) in skeletal muscles and brain of many vertebrates. We have demonstrated in a previous work that these compounds can act as antioxidants, a result of their ability to scavenge peroxyl radicals, singlet oxygen and hydroxyl radicals. Carnosine and its analogues have been shown to be efficient chelating agents for copper and other transition metals. Since human skeletal muscle contains one-third of the total copper in the body (20-47 mmol/kg) and the concentration of carnosine in this tissue is relatively high, the complex of carnosine:copper may be of biological importance. We have studied the ability of the copper:carnosine (and other carnosine derivatives) complexes to act as superoxide dismutase. The results indicate that the complex of copper:carnosine can dismute superoxide radicals released by neutrophils treated with PMA in an analogous mechanism to other amino acids and copper complexes. Copper:anserine failed to dismute superoxide radicals and copper:homocarnosine complex was efficient when the cells were treated with PMA or with histone-opsonized streptococci and cytochalasine B. The possible role of these compounds to act as physiological antioxidants that possess superoxide dismutase activity is discussed.

Leishmania major: inhibition of the chemiluminescent response of human polymorphonuclear leukocytes by promastigotes and their excreted factors

The effect of various leishmanial preparations on the chemiluminescent response (CR) of human polymorphonuclear leukocytes (PMN) was studied. Almost no CR was observed with PMN stimulated with either Leishmania promastigotes or their excreted factors (EFs). Promastigotes added to PMN stimulated with phorbol myristate acetate (PMA), at a proportion of 20 to 1, respectively inhibited approximately 80-83% of the CR activity. Leishmanial promastigotes, whether live or dead, infective or non-infective as well as whole parasite homogenates, soluble and insoluble fractions, all decreased the CR of the PMN (PMN-CR). A similar effect was also observed with leishmanial EFs. The degree of inhibition was dose dependent and increasing the amount of EFs in the reaction mixture resulted in decrease of the PMN-CR. More than 80% of the total activity of the PMN-CR was inhibited by 500 micrograms EFs added at zero time to the reaction mixture. The inhibition of PMN-CR obtained from a patient suffering from a chronic infection caused by L. major was not significantly different from that observed with PMN from normal donors. The present study suggests that the PMN-CR is impaired by the Leishmania parasites and their EFs and thus may allow a greater survival of the parasites within these cells.

Interaction of mammalian cells with polymorphonuclear leukocytes: relative sensitivity to monolayer disruption and killing

Monolayers of murine fibrosarcoma cells that had been treated either with histone-opsonized streptococci, histone-opsonized Candida globerata, or lipoteichoic acid-anti-lipoteichoic acid complexes underwent disruption when incubated with human polymorphonuclear leukocytes (PMNs). Although the architecture of the monolayers was destroyed, the target cells were not killed. The destruction of the monolayers was totally inhibited by proteinase inhibitors, suggesting that the detachment of the cells from the monolayers and aggregation in suspension were induced by proteinases releases from the activated PMNs. Monolayers of normal endothelial cells and fibroblasts were much resistant to the monolayer-disrupting effects of the PMNs than were the fibrosarcoma cells. Although the fibrosarcoma cells were resistant to killing by PMNs, killing was promoted by the addition of sodium azide (a catalase inhibitor). This suggests that the failure of the PMNs to kill the target cells was due to catalase inhibition of the hydrogen peroxide produced by the activated PMNs. Target cell killing that occurred in the presence of sodium azide was reduced by the addition of a "cocktail" containing methionine, histidine, and deferoxamine mesylate, suggesting that hydroxyl radicals but not myeloperoxidase-catalyzed products were responsible for cell killing. The relative ease with which the murine fibrosarcoma cells can be released from their substratum by the action of PMNs, coupled with their insensitivity to PMN-mediated killing, may explain why the presence of large numbers of PMNs at the site of tumors produced in experimental animals by the fibrosarcoma cells is associated with an unfavorable outcome.

Permeabilization and calcium-dependent activation of rabbit polymorphonuclear leukocytes by poly-L-arginine

In the absence of extracellular Ca2+, poly-L-arginine induces little lysozyme release from rabbit polymorphonuclear leukocytes (PMNs). The polycation causes plasma membrane damage, which is evident from the release of the cytoplasmic enzyme lactate dehydrogenase (LDH). In the presence of Ca2+ concentrations higher than 0.2 mM, poly-L-arginine induces a strong lysozyme release that is superimposed on the membrane-damaging effect. The results suggest that poly-L-arginine permeabilizes the plasma membrane, enabling Ca2+ to enter the cell, which results in the exocytotic release of granule constituents. The GTP analog GTP gamma S shifts the Ca2+ requirement of exocytosis to slightly higher concentrations, whereas it completely inhibits poly-L-arginine-induced LDH release. Pertussis toxin gives a moderate inhibition, and La3+ completely inhibits poly-L-arginine-induced enzyme release. Whereas poly-L-arginine alone induces little superoxide generation in rabbit PMNs, there is a synergistic enhancement of superoxide production when GTP gamma S and poly-L-arginine are present together. Guanine nucleotides apparently have a modulating effect on the actions of poly-L-arginine on the PMN, but the nature of this effect remains to be determined.

Lysophosphatides enhance superoxide responses of stimulated human neutrophils

Human neutrophils which are pretreated with subtoxic concentrations of a variety of lysophosphatides (lysophosphatidylcholine, lysophosphatidylcholine oleoyl, lysophosphatidylcholine myrioyl, lysophosphatidylcholine stearoyl, lysophosphatidylcholine gamma-O-hexadecyl, lysophosphatidylinositol, and lysophosphatidylglycerol) act synergistically with neutrophil agonists phorbol myristate acetate, immune complexes, poly-L-histidine, phytohemagglutinin, and N-formyl-methionyl-leucyl-phenyalanine to cause enhanced generation of superoxide (O2-). None of the lyso compounds by themselves caused generation of O2-. The lyso compounds strongly bound to the neutrophils and could not be washed away. All of the lyso compounds that collaborated with agonists to stimulate O2- generation were hemolytic for human red blood cells. On the other hand, lyso compounds that were nonhemolytic for red blood cells (lysophosphatidylcholine caproate, lysophosphatidylcholine decanoyl, lysophosphatidylethanolamine, lysophosphatidylserine) failed to collaborate with agonists to generate synergistic amounts of O2-. However, in the presence of cytochalasin B, both lysophosphatidylethanolamine and lysophosphatidylserine also markedly enhanced O2- generation induced by immune complexes. O2- generation was also very markedly enhanced when substimulatory amounts of arachidonic acid or eicosapentanoic acid were added to PMNs in the presence of a variety of agonists. On the other hand, neither phospholipase C, streptolysin S (highly hemolytic), phospholipase A2, phosphatidylcholine, nor phosphatidylcholine dipalmitoyl (all nonhemolytic) had the capacity to synergize with any of the agonists tested to generate enhanced amounts of O2-. The data suggest that in addition to long-chain fatty acids, only those lyso compounds that possess fatty acids with more than 10 carbons and that are also highly hemolytic can cause enhanced generation of O2- in stimulated PMNs.

Cationic polyelectrolytes: potent opsonic agents which activate the respiratory burst in leukocytes

Bacteria and yeasts which are "opsonized" with cationic polyelectrolytes (poly-L-arginine, poly-L-histidine and arginine-rich histone) are avidly endocytosed by both "professional" and "non-professional" phagocytes. The cationized particles also strongly activate the respiratory burst in neutrophils and in macrophages leading to the generation of chemiluminescence, superoxide and hydrogen peroxide. On the other hand, lysine and ornithine-rich polymers are poor opsonic agents. Poly L-arginine is unique in its capacity to act synergistically with lectins, with chemotactic peptides and with cytochalasin B to generate large amounts of chemiluminescence and superoxide in human neutrophils. Unlike polyarginine, polyhistidine, in the absence of carrier particles, is one of the most potent stimulators of superoxide generations, known. Neutrophils treated with cetyltrimethylammonium bromide fail to generate superoxide, but generate strong luminol-dependent chemiluminescence which is totally inhibited by sodium azide and by thiourea. Neutrophils injured by cytolytic agents (saponin, digitonin, lysolecithin) lose their chemiluminescence and superoxide-generating capacities upon stimulation by a variety of ligands. These activities are however regained by the addition of NADPH. Lysolecithin can replace polyarginine in a "cocktail" also containing lectins and cytochalasin B, which strongly activate the respiratory burst. This suggests that polyarginine acts both as a cytolytic agent and as a ligand. Arginine and histidine-rich polyelectrolytes enhance the pathogenic effects of immune complexes in vivo (reversed Arthus phenomenon) presumably by "glueing" them to tissues. Polyhistidine complexed to catalase or to superoxide dismutase, markedly enhances their efficiency as antioxidants. On the other hand polyhistidine complexed to glucose oxidase markedly enhances injury to endothelial cells suggesting that the close association of the cationized enzyme with the plasma membrane facilitates the interaction of hydrogen peroxide with the targets. A variety of cationic agents (histone, polyarginine, polyhistidine, polymyxin B) and membrane-active agents (lysophosphatides, microbial hemolysins) act synergistically with glucose oxidase or with reagent hydrogen peroxide to kill target cells. The mechanisms by which arginine- and histidine-rich polyelectrolytes activate the respiratory burst in neutrophils might involve interaction with G-proteins, the activation of arachidonic acid metabolism and phospholipase A2, or the interaction with myeloperoxidase. Naturally-occurring cationic proteins might modulate several important functions of leukocytes and the course and outcome of the inflammatory process.

Lipoteichoic acid-antilipoteichoic acid complexes induce superoxide generation by human neutrophils

Human neutrophils (PMNs) which have been incubated with lipoteichoic acid (LTA) from group A streptococci generated large amounts of superoxide (O2- chemiluminescence and hydrogen peroxide when challenged with anti-LTA antibodies. Cytochalasin B further enhanced O2- generation. The onset of O2- generation by the LTA-anti-LTA complexes was much faster than that induced by BSA-anti-BSA complexes. LTA-treated PMNs generated much less O2- when challenged with BSA complexes, suggesting that LTA might have blocked, nonspecifically, some of the Fc receptors on PMNs. PMNs treated with LTA-anti-LTA complexes further interacted with bystander nonsensitized PMNs resulting in enhanced O2- generation, suggesting that small numbers of LTA-sensitized PMNs might recruit additional PMNs to participate in the generation of toxic oxygen species. Protelolytic enzyme treatment of PMNs further enhanced the generation of O2- by PMNs treated with LTA-anti-LTA. Superoxide generation could also be induced when PMNs and anti-LTA antibodies interacted with target cells (fibroblasts, epithelial cells) pretreated with LTA. This effect was also further enhanced by pretreatment of the target cells with proteases. PMNs incubated with LTA released lysosomal enzymes following treatment with anti-LTA antibodies. The amounts of phosphatase, beta-glucoronidase, N-acetylglucosaminidase, mannosidase, and lysozyme release by LTA-anti-LTA complexes were much smaller than those released by antibody or histone-opsonized streptococci, suggesting that opsonized particles are more efficient lysosomal enzyme releasers. However, since the amounts of O2- generated by the LTA complexes equaled those generated by the opsonized particles, it is assumed that the signals for triggering a respiratory burst and lysosomal enzyme secretion might be different. Generation of O2- by LTA complexes was strongly inhibited by lipoxygenase inhibitors but not by cyclooxigenase inhibitors. Also phenylbutazone, trifluorperazine, and DASA markedly inhibited O2- generation induced by LTA complexes. These data suggest that bacterial products in the presence of antibody might have important biological effects on phagocytic cells and that these effects may be inimical to the host.

The role of oxygen radicals in immune complex injury

In this review we will summarize our current understanding of the mediation of immune complex induced tissue injury. Comparisons will be made between the mediation of IgG versus IgA immune complex injury with emphasis on the role that reactive oxygen products derived from leukocytic phagocytic cells play in the initiation of the tissue injury.

Poly L-histidine. A potent stimulator of superoxide generation in human blood leukocytes

Poly-L-histidine (PHSTD) of molecular weight 26,000 induced the generation of large amounts of superoxide (O2-) and hydrogen peroxide (H2O2) in human neutrophils (PMNs). Despite its low solubility at neutral pH, PHSTD was bound very rapidly to the PMN surfaces. Maximal generation of O2- took place with 4-5 X 10(-6) M of PHSTD, starting after a lag of about 25 sec and proceeding for 15-17 min at a rate of 150 nmol/10(7) PMNs/min, suggesting that this polycation is one of the most potent stimulators of O2- generation known, PHSTD was found to be non-toxic for PMNs even at millimolar concentrations. Generation of O2- by PHSTD depended on extracellular calcium; it was inhibited by calcium channel blockers and by trifluoperazine, and it triggered a sharp rise in intracellular calcium as determined by the Quin 2 fluorescence technique. The generation of both O2- and H2O2 by PHSTD was partially inhibited by cytochalasin B or (CYB, CYE). On the other hand, CYB markedly enhanced the generation of both O2- and H2O2 following stimulation of PMNs either by PHSTD, polyarginine, histone, or by antibody-opsonized group A streptococci. Electron microscopic analysis and NBT reduction tests revealed that both PHSTD and PHSTD-opsonized streptococci were avidly phagocytosed by PMNs. Since CYB totally inhibited internalization of both PHSTD and the PHSTD-opsonized streptococci, it was suggested that these agents stimulated oxygen radical generation mainly on the leukocyte surfaces. Complexes (CX) formed between PHSTD and polyanethole sulfonate (a strong polyanion) or between histone and the polyanion mimicked immune CX in their ability to trigger the generation of large amounts of O2- which were inhibited by CYB. Generation of O2- and chemiluminescence either by PHSTD or by PHSTD-opsonized streptococci were markedly inhibited by poly-L-glutamate, suggesting that PHSTD acted as a cationic agent which interacted via electrostatic forces with some negatively charged sites in the leukocyte membrane. Generation of H2O2 by PHSTD was also markedly inhibited by deoxyglucose, KCN, DASA, as well as by the lipoxygenase inhibitors nordihydroguaiaretic acid, phenidone, and propylgallate. On the other hand, cyclooxygenase inhibitors such as aspirin, indomethacin, and piroxicam were inactive, suggesting that arachidonic acid metabolism via lipoxygenase pathway might have been involved in the activation by PHSTD of the NADPH oxidase in PMNs.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of superoxide generation by human polymorphonuclear leukocytes with chlorhexidine. Its possible relation to periodontal disease

During the acute phase of periodontal disease, as many as 60% of the cells of the junctional epithelium may be accounted for by polymorphonuclear cells (PMNs). It is generally accepted that these cells play a dominant role in the destruction of connective tissue by virtue of the proteinases they release and the free oxygen radicals they generate. Modulation of the proteolytic activity and free radical production seems to be essential for the inhibition of tissue destruction. We have therefore studied the effect of chlorhexidine on the generation of free oxygen radicals and luminol-dependent chemiluminescence (LDCL) by stimulated human PMNs. Nontoxic chlorhexidine concentrations (0.1-1 microgram/ml) were found to inhibit superoxide production but did not affect LDCL. We therefore suggest that in addition to its antiseptic effect, chlorhexidine may also modulate the generation of free radicals by activated PMN cells in the inflamed gingiva.

NADPH and "cocktails" containing polyarginine reactivate superoxide generation in leukocytes lysed by membrane-damaging agents

Human blood leukocytes generated large amounts of superoxide (O2-) following stimulation by certain "cocktails" of soluble agents consisting of poly-L-arginine (PARG), phytohemagglutinin, the chemotactic peptide formyl-methionyl-leucyl-phenylalanine and polyanethole sulfanote (liquoid). A variety of cytochalasins, which markedly boosted O2- generation by the soluble cocktails, markedly depressed luminol-dependent chemiluminescence (LDCL) which had been induced either by opsonized streptococci or by soluble agents. Glutathione, which totally reversed the inhibition of LDCL induced by cytochalasin A, failed to reverse the inhibition of LDCL induced by cytochalasin B. Generation of O2- by all the soluble agents employed, except PMA, was strongly inhibited either by the omission of extracellular calcium and magnesium or by treatment with the calcium blocker TMB-8. Generation of O2- was enhanced following stimulation of leukocytes with soluble agents if the cells had been exposed to slightly hypotonic buffers. Leukocytes, which had been preincubated for short periods (5 min) with PARG, saponin, digitonin, or lysolecithin (LL) and which lost their viability, and their O2- and LDCL-generating capacities following stimulation by soluble agents containing cytochalasin B, nevertheless regained these activities by the addition of NADPH. It is suggested that the lytic agents induced the leakage out of NADPH rather than acting as inactivators of the oxidase in the leukocyte membranes. Prolonged incubation of leukocytes with lytic agents failed to allow restoration, by NADPH, of the generation of SOD-inhibitable O2- generation. Since PARG acted both as a cytolytic agent and as a inducer of O2- generation, we postulate that lytic agents might also act as "primers" of the nascent membrane oxidase which could, however, be further potentiated and activated by soluble agents acting in "multiple hits," PARG could be totally replaced either by LL or by digitonin in the generation of O2- provided that both PHA and cytochalasin B were present in the reaction mixtures. We suggest that the various ingredients of the soluble "cocktails" may help to assemble components of the NADPH oxidase. Such an assembly and regulations are prerequisite for stimulation of the NADPH oxidase and the generation of oxygen radicals in leukocytes.