Polyamino acid enhancement of bacterial phagocytosis by human polymorphonuclear leukocytes and peritoneal macrophages

Design, synthesis, and biocompatibility of an arginine-based polyester

Polycations are very useful in biotechnology. However, most existing polycations have high toxicity that significantly limits their clinical translation. We designed poly(ethylene argininylaspartate diglyceride) (PEAD) that is based on arginine, aspartic acid, glycerol, and ethylene glycol. A set of in vitro assays demonstrated that PEAD exhibited no cytotoxicity at 1 mg/mL, which is at least 100 times higher than the widely used polycation-polyethylenimine. Subcutaneous injection of 1 mg PEAD in rats did not cause an adverse response acutely or after 4 weeks. Zeta potential measurements revealed that PEAD has high affinity to biological polyanions such as DNA and hyaluronic acid. This polycation represents a new platform of biocompatible polycations that may lead to clinical innovations in gene therapy, controlled release, tissue engineering, biosensors, and medical devices.

Effects of sub-minimal inhibitory concentrations of antimicrobial agents on the cell surface of Klebsiella pneumoniae and phagocytic killing activity

Changes in the phagocytic killing activity, capsule structure, and physicochemical properties such as the hydrophobicity and charge of the cell surface were studied in Klebsiella pneumoniae treated with sub-minimal inhibitory concentrations (MICs) of various antimicrobial agents. The phagocytic killing activity of macrophages was enhanced by penicillins, cephems, and monobactam in the absence of antibodies specific to the capsule or complement. No enhancement was observed with new quinolones, aminoglycosides, macrolide, or carbapenem. The thickness of the capsule structure was considerably reduced after the treatment with penicillins, cephems, and monobactam compared with the untreated control, and it was slightly reduced by new quinolones. No changes were observed in the capsule structure with aminoglycosides, macrolide, and carbapenem. The hydrophobicity on the cell surface of the bacteria was considerably increased after the treatment with penicillins, cephems, and monobactam compared with the control, slightly increased with new quinolones and carbapenem, and not changed with aminoglycosides and macrolide. The negative charge of the cell surface of the bacteria was reduced by penicillins, cephems, and monobactam compared with the control. It was slightly reduced by new quinolones and carbapenem but was not reduced by aminoglycosides and macrolide. These findings suggest that sub-MIC beta-lactam drugs such as penicillins, cephems, and monobactams cause thinning of the capsule of K. pneumoniae with increases in the hydrophobicity and decreases in the negative charge of the cell surface, which reduces the physical repulsion between the K. pneumoniae and phagocytes and enhances the sensitivity of the bacteria to phagocytic killing activity.

The role of calcium ions in DEAE-dextran-induced stimulation of neutrophil migration

The polycation DEAE-dextran caused a strong enhancement of non-directed migration of rabbit peritoneal neutrophils. The activating effect on migration was completely annulled in the presence of the polyanion poly-D-glutamic acid, indicating that the effect depended on the positive charge of the macromolecule. Chemotaxis activated by the chemotactic peptide fMLP was only slightly affected by the polycation. In contrast with fMLP-activation, stimulation of migration by DEAE-dextran was dependent on the presence of extracellular Ca2+. DEAE-dextran also stimulated migration of electroporated neutrophils. The stimulation was absent when calcium was not present; the increase of migration was strongest at Ca(2+)-concentrations between 100 nM and 1 microM Ca2+. This indicates that the requirement for extracellular Ca2+ in intact cells is a reflection of the intracellular requirement. Several types of calcium blockers gave a moderate inhibition of DEAE-dextran activated migration. Activation of migration by DEAE-dextran of electroporated neutrophils was completely inhibited by calcium channel blockers, at very low concentrations. The results suggest that both Ca(2+)-fluxes across the plasma membrane and Ca2+ from intracellular stores are required for DEAE-activated migration, and that the calcium from the intracellular source is required on a place where the extracellular Ca2+ has no, or limited, admittance.

Identification of macrophage cell-surface binding sites for cationized bovine serum albumin

Autoimmune diseases are characterized by the presence of autoantibodies often restricted to host proteins exhibiting charge rich domains. Charged polypeptides elicit strong immune responses, and cationized bovine serum albumin and other cationic proteins are significantly more immunogenic than their less charged counterparts. These phenomena may involve enhanced protein uptake by macrophages, resulting in greater processing and presentation of antigenic peptide-MHC complexes to T-cells. We compared macrophage cell-surface binding and uptake of native and cationized bovine serum albumin. Specific binding of [125I]cationized bovine serum albumin to THP-1 macrophages in vitro was 11-16 fold greater than for native albumin. Half-maximal inhibition of [125I]cationized albumin binding was observed at 10-7M ligand. The specificity of [125I]cationized bovine serum albumin binding and uptake was further studied in terms of competitive inhibition of proteolysis by proteins of varying charge content. Cationized bovine serum albumin, but not native albumin, inhibited proteolysis of [125I]cBSA. Calf thymus histones also inhibited cBSA degradation. High concentration of myelin basic protein was moderately effective at blocking cBSA degradation, while myoglobin and beta lactalbumin showed no inhibition. These results indicate that specific cell-surface binding sites which occur on macrophages may mediate selective uptake of certain proteins with highly charged domains including some autoantigens.

Very long charge runs in systemic lupus erythematosus-associated autoantigens

Systemic lupus erythematosus and other chronic systemic autoimmune diseases are associated with circulating autoantibodies reactive with a limited set of mostly nuclear proteins. Using rigorous statistical methods we have identified segments of highly significant charge concentration in the majority of the characteristic nuclear and cytoplasmic autoantigens. Extremely long runs of charged residues, including some sequences of greater than 20 consecutive charged residues (purely acidic or mixed basic and acidic), occur in about a third of these proteins, whereas equivalent runs are found in less than 3% of other mammalian proteins. The other sequences have less extreme charge clusters, the type and location of which are often conserved between several otherwise nonsimilar antigens. We propose that supercharged surfaces render the targeted host proteins strongly immunogenic and that antinuclear antibody profiles might result from chronic exposure to intracellular contents, possibly in conjunction with crossreactive viral products. The limited number of potential systemic autoantigens may partly be due to the rarity of requisite charge properties.

Charge distributions and amphipathicity of receptor-binding alpha-helices

Contacts between ligands and cell-surface receptors result in cellular activation. Defining principles which govern these important interactions are of interest and might facilitate pharmacologic intervention. We examined receptor-binding alpha-helical segments of polypeptide hormones and globular proteins for distinguishing amino acid content and distributions. There was a slight excess of basic residues in both sets of alpha-helices compared with a panel of control helices. Helical concentrations of charged residues were quantitated using the hydrophobic moment algorithm, adapted to obtain the vector sum of side chain charges. By this analysis we detected increased concentrations of the set of basic residues (arginine, lysine and histidine) on one side of the receptor-binding alpha-helices of the polypeptide hormones, and to a lesser extent the protein ligands. Comparable data were obtained for "lytic" venom peptides and calmodulin-regulated kinase segments. There was an even greater correlation between receptor-associating alpha-helical segments and large hydrophobic moments. Receptor-binding helical segments of polypeptide hormones, and to a lesser extent those of protein ligands, often are basic and amphipathic.

The influence of net surface charge on the interaction of uropathogenic Escherichia coli with human neutrophils

Escherichia coli strains, grown to suppress fimbrial expression, synthesised enhanced quantities of polysaccharide capsule, which significantly lessened their binding to heparin sepharose columns. In the presence of poly-L-lysine, these strains were strongly retained on the columns confirming their highly anionic nature. Uropathogenic strains of E. coli expressing type 1 fimbrial adhesins activated the respiratory burst, the degranulation response and the release of leukotrienes from human neutrophils (PMN) to a significantly greater extent than the same strains grown in a medium to suppress this fimbrial expression. The addition of the poly-cation poly-L-lysine, however, selectively increased neutrophil activation in response to these non-fimbriate strains. This dose-dependent effect was reversed by the addition of heparin suggesting a mechanism dependent on surface charge. The results of this study suggest that non-specific mechanisms involving the neutralisation of surface charge, in addition to specific receptor and adhesin mediated events could affect neutrophil activation at sites of infection.

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.

The antimicrobial activity of protamine and polybrene

Polybrene and protamine have broad antimicrobial activity and may be useful as topical agents.

Protamine sulfate-induced enzyme secretion from rabbit neutrophils

Protamine sulfate induces enzyme secretion from rabbit neutrophils. Enzyme secretion is mainly due to exocytosis but, depending on the experimental conditions, a small amount of cytolysis may occur. As compared with stimulation of neutrophil functions by other activators, protamine sulfate-induced enzyme release by exocytosis is a relatively slow process and is not accompanied by a marked activation of the metabolic burst. For optimal exocytosis, extracellular Ca2+ is required, but there is still some enzyme release in its absence, and other metal ions (Sr2+, Ba2+, Mg2+) can partly mimic the effect of Ca2+. Positive charges on protamine are of primary importance because the polyanion heparin completely inhibits protamine sulfate-induced enzyme release. Protamine linked to agarose beads is able to induce enzyme release; thus the induction of exocytosis is due to an interaction of the positive charges on protamine with the plasma membrane. Sialic acid residues on the membrane, however, seem not to play an important role in this process.

Augmentation of host defense by a unicellular green alga, Chlorella vulgaris, to Escherichia coli infection

Protection against Escherichia coli inoculated intraperitoneally into mice was enhanced by intraperitoneal, intravenous, or subcutaneous administration of a water-soluble, high-molecular-weight fraction extracted from a dialyzed hot-water extract from a strain of Chlorella vulgaris (CVE-A). The enhancing effect was detected with doses over 2.0 mg/kg and when doses were administered 1, 4, or 7 days before the infection. The elimination of bacteria from the spleen of CVE-A-treated mice was increased, and this enhanced elimination may have been related to the acceleration of superoxide generation and chemokinesis in polymorphonuclear leucocytes by CVE-A treatment. A cyclophosphamide-induced decrease in protection against E. coli could be prevented by subcutaneous administration of CVE-A.

Human peritoneal macrophages: clinical models of inflammation and potential targets of antiinflammatory drugs

Human peritoneal macrophages have been obtained from patients with renal disease undergoing chronic peritoneal dialysis, patients with ascites and at laparoscopy. These macrophages in general have both morphological and enzymatic characteristics of activated macrophages, as judged by criteria derived from animal experiments. Human peritoneal macrophages produce a variety of eicosanoids, including leukotriene B4 and leukotriene C4. These cells are suitable for studies on in vitro and in vivo effects of drugs, and for investigation of changes in macrophage activity occurring in human diseases.

Modulation of locomotor activity of polymorphonuclear cells by cationic substances and cationic lysosomal fractions from human neutrophils

Seven cationic substances--human and egg-white lysozyme, RNase, protamine, histone, poly-L-lysine and poly-L-arginine; five cationic lysosomal fractions from human polymorphonuclears (PMNs); RNA; poly-L-glutamic acid; DNA; heparin; endotoxin; mastocytotropic agent compound 48/80; and cytochalasin B were tested for the influence on chemotaxis and random migration of human PMNs using under-agarose migration and Boyden chambers with two filters and [51Cr]PMNs. The above substances were either preincubated with PMNs, added to chemoattractants, or used instead of chemoattractants. In under-agarose migration method chemotaxis was inhibited by 11-35% when egg-white lysozyme, protamine, heparin, endotoxin, or compound 48/80 was added to the cells. High concentration of cytochalasin B inhibited chemotaxis by 73%. Cationic fractions I and V and low concentration of cytochalasin B enhanced chemotaxis by 11%, 41%, and 30%, respectively. When human and egg-white lysozyme, DNA, or cytochalasin B was added to the chemoattractants, motility of PMNs was inhibited. Cationic fractions II and V from human PMNs, when used as chemoattractants, enhanced cellular motility by 143-167%. Random migration was enhanced by heparin and inhibited by cytochalasin B and by cationic fractions from human PMNs. These findings suggest that various cationic and anionic substances and cationic fractions from human PMNs have heterogeneous influence on random migration and chemotactic activity of human PMN. Analysis relating chemotaxis to phagocytosis and to intracellular bactericidal activity (ICBA) has shown several patterns. Protamine, poly-L-lysine, poly-L-arginine, and agent compound 40/80 all inhibit chemotaxis and enhance phagocytosis and ICBA; cationic fractions II and V enhanced all three functions, whereas cytochalasin B suppressed phagocytosis and ICBA and had concentration-dependent modulatory influence on chemotaxis. It implies diverse mechanisms of action and possible impact on inflammatory reactions.

Cytolytic effect of polylysine on rabbit polymorphonuclear leukocytes

The cationic polyamino acids polylysine and polyarginine cause a time and concentration dependent lysis of rabbit polymorphonuclear leukocytes. Lysis, measured as LDH release, is preceded by exocytosis, as can be deduced from a higher lysozyme release than LDH release, at short incubation time or with low concentrations of polylysine. The lytic effect of polylysine could be annihilated with the polyanion polyglutamic acid. Monomeric lysine or arginine, or low-molecular-weight polylysine, were not lytic. This indicates that positive charges on a polymeric molecule of sufficient chain length play a predominant role in the interaction. Substances that promote exocytosis cause an increase of lysozyme release and a reduction of LDH release, whereas inhibitors of exocytosis cause the reverse: less lysozyme release and more LDH release. Negatively charged sialic groups on the plasma membrane are not important for the interaction, because their removal does not affect the lytic effect of polylysine on the cell. The possibility that the lipid part of the plasma membrane is the point of attack for the polycations is discussed.

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

Human blood leukocytes generate intense luminol-dependent chemiluminescence (LDCL) following stimulation by streptococci and by Gram negative rods which had been preopsonized by cationic polyelectrolytes (histone, poly L-arginine-PARG, poly L-histidine-PHSTD). Streptococci but not Gram negative rods or hyaluronic acid-rich streptococci (group C) also induced intense LDCL following opsonization with the anionic polyelectrolytes-dextran sulfate or polyanethole sulfonate (liquoid) suggesting that the outer surfaces of different bacteria bound anionic polyelectrolytes to different extents. Both normal and immune serum, synovial fluids and pooled human saliva inhibited the LDCL responses induced by streptococci preopsonized with poly cations. On the other hand, bacteria which had been first preopsonized by the various body fluids and then subjected to a second opsonization by cationic ligands ("sandwiches"), induced a very intense LDCL response in leukocytes. Streptococci which had been preopsonized by PARG, histone or by PHSTD also triggered superoxide generation by blood leukocytes, which was markedly enhanced by a series of cytochalasins. PHSTD alone induced the formation of very large amounts of superoxide. Paradoxically, the same concentrations of cytochalasins B or C which markedly boosted the generation of superoxide following stimulation of leukocytes with soluble or particulate ligands, had a strong inhibitory effect on the generation of LDCL. On the other hand cycochalasins failed to inhibit LDCL which had been induced by phorbol myristate acetate (PMA). Peritoneal macrophages which had been harvested from C. parvum-stimulated mice, generated more LDCL and superoxide following stimulation by PARG than macrophages obtained from proteose peptone-stimulated mice. Macrophages which had been activated either by proteose peptone or by C. parvum and cultivated for 2 hours on teflon surfaces, generated much more LDCL than macrophages which had been cultivated for 24 hours on teflon surfaces. Both cationic and anionic polyelectrolytes mimic the effects of antibodies as activators of the oxygen burst in blood leukocytes and in macrophages. Such polyelectrolytes can serve as models to further study leukocyte-bacteria interactions in infectious and inflammatory sites.

Antimicrobial activities of dialysate-elicited and resident human peritoneal macrophages

Recent studies of the antimicrobial capacity of peritoneal macrophages (PM phi) isolated from patients undergoing chronic peritoneal dialysis have raised the question of whether these cells might be analogous to stimulated or activated murine PM phi. To explore this possibility, we compared PM phi from these patients (dialysate-elicited PM phi) with PM phi obtained from women undergoing laparoscopy (resident PM phi) in several in vitro assays of phagocyte function. Although bacterial phagocytosis by cells from both groups of donors was similar, significant differences were found in their chemiluminescence responses to opsonized zymosan. Although the mean peak luminol-enhanced chemiluminescence response of dialysate-elicited PM phi was 4.7 X 10(5) cpm, that of resident PM phi was only 1.3 X 10(5) cpm (P less than 0.05). In a lucigenin-enhanced chemiluminescence assay, dialysate-elicited PM phi again generated significantly greater chemiluminescence than did resident PM phi, suggesting that dialysate-elicited PM phi have a relatively increased capacity for O2- production. Using a fluorochrome microassay to assess the intracellular candidicidal activities of these cells, we found that dialysate-elicited PM phi killed 17% of cell-associated blastospores compared with only 1.5% killing by resident PM phi (P less than 0.05). These investigations led us to conclude that results of studies of the functional activity of dialysate-elicited PM phi cannot necessarily be extrapolated to resident PM phi and that dialysate-elicited PM phi do in some respects behave as stimulated or activated cells.

Purification and characterization of a phagocytosis-stimulating factor from phagocytosing polymorphonuclear neutrophils: comparison with granule basic proteins

Phagocytosis-stimulating factor (PSF) was purified by copper chelate chromatography and characterized in comparison with basic proteins in the granule of polymorphonuclear neutrophils. By copper chelate chromatography, PSF was eluted at pH 3.7; whereas cationic protein, lysozyme, and lactoferrin were eluted at pH 5.6, 5.1, and 4.0, respectively. Purified PSF has an approximate molecular weight of 16,000 and an isoelectric point at 8.7, which differ from those of basic proteins, such as cationic protein, lysozyme, and lactoferrin. Anionic substances such as DNA and heparin did not influence the phagocytosis-stimulating activity of PSF, whereas that of the granule basic protein fraction from resting polymorphonuclear neutrophils was abolished. PSF had little bactericidal activity against Escherichia coli and Staphylococcus aureus, whereas the granule basic protein fraction from resting PMNs had strong bactericidal activity against E. coli and weak activity against S. aureus. These results indicate that PSF is a basic protein which is distinguishable from cationic protein, lysozyme, and lactoferrin.

Opsonic activity of MCP-1 and MCP-2, cationic peptides from rabbit alveolar macrophages

MCP-1 and MCP-2, cationic peptides derived from rabbit alveolar macrophages, enhanced the ability of these cells to ingest Staphylococcus aureus, Klebsiella pneumoniae, Bordetella bronchiseptica, and Candida albicans in vitro. The opsonic effect of MCP-1 was potentiated by Ca++ and Mg++ and was associated with binding of the peptide to alveolar macrophages and microorganisms. MCP-1 and MCP-2 may contribute to the ability of alveolar macrophage to ingest microorganisms that gain entry to the lower respiratory tract.

Influence of nutrient limitation and low pH on serogroup B Neisseria meningitidis capsular polysaccharide levels: correlation with virulence for mice

Neisseria meningitidis strain M986, which possesses a polyanionic sialic acid capsular polysaccharide, was resistant to the bactericidal effects of normal rabbit serum, but sensitive when immune serum and complement were present. An isogenic strain PRM102, deficient in the ability to produce capsular polysaccharide, was sensitive to normal serum. Strain M986, when grown under conditions of low pH or nutrient limitation, synthesized increased levels of capsular polysaccharide. This was accompanied by an increase in cell surface hydrophilicity and virulence for mice. Cells grown in low-pH, iron-limited medium synthesized the highest concentration of polysaccharide and exhibited the highest cell surface hydrophilicity and virulence among the cases examined. The increase in capsular polysaccharide was partly explained by a decrease in the specific activity of a membrane-bound cytidine monophosphate-N acetylneuraminic acid hydrolase. The results suggest that conditions of nutrient limitation and low pH exert profound effects on the physicochemical nature of the meningococcal cell surface which, in turn, cumulate in enhanced virulence of this organism for mice.