Effect of leukocyte hydrolases on bacteria XVI. Activation by leukocyte factors and cationic substances of autolytic enzymes in Staphylococcus aureus: modulation by anionic polyelectrolytes in relation to survival of bacteria in inflammatory exudates

Bactericidal cationic peptides can also function as bacteriolysis-inducing agents mimicking beta-lactam antibiotics?; it is enigmatic why this concept is consistently disregarded

Although there is a general consensus that highly cationic peptides kill bacteria primarily by injuring their membranes, an additional hypothesis is proposed suggesting that a large variety of cationic peptides might also render bacteria non viable by activating their autolytic wall enzymes - muramidases (a "Trojan Horse" phenomenon), resulting in bacteriolysis. This group of cationic peptides includes: lysozyme, lactoferrin, neutrophil-derived permeability increasing peptides, defensins, elastase, cathepsin G, and secretory phopholipase A2. In this respect, cationic peptides mimic the bactericidal/bacteriolytic effects exerted by of beta-lactam antibiotics. Bacteriolysis results in a massive release of the pro-inflammatory cell-wall components, endotoxin (LPS), lipoteichoic acid (LTA) and peptidoglycan (PPG), which if not effectively controlled, can trigger the coagulation and complement cascades, the release from phagocytes of inflammatory cytokines, reactive oxygen and nitrogen species, and proteinases. Synergism (a "cross-talk") among such agonists released following bacteriolysis, is probably the main cause for septic shock and multiple organ failure. It is proposed that a use of bacteriolysis-inducing antibiotics should be avoided in bacteremic patients and particularly in those patients already suspected of developing shock symptoms as these might further enhance bacteriolysis and the release of LPS, LTA and PPG. Furthermore, in additonal to the supportive regimen exercised in intensive care settings, a use of non bacteriolysis-inducing antibiotics when combined with highly sulfated compounds (e.g. heparin, and other clinically certified polysufates) should be considered instead, as these might prevent the activation of the microbial own autolytic systems induced either by highly cationic peptides released by activated phagocytes or by the highly bacteriolytic beta-lactams. Polysulfates might also depress the deleterious effects of the complement cascade and the use of combinations among anti-oxidants ( N-acetyl cysteine), proteinase inhibitors and phospholipids might prove effective to depress the synergistic cytotoxic effects induced by inflammatory agonists. Also, a use of gamma globulin enriched either in anti-LPS or in anti-LTA activities might serve to prevent the binding of these toxins to receptors upon macrophage which upon activation generate inflammatory cytokines. Thus, a use of "cocktails" of anti-inflammatory agents might replace the unsuccessful use of single antagonists proven in scores of clinical trials of sepsis to by ineffective in prolonging the lives of patients. It is enigmatic why the concept, and the publications which support a role for cationic peptides also as potent inducers of bacteriolysis, an arch evil and a deleterious phenomenon which undoubtedly plays a pivotal role in the pathophysiology of post-infectious sequelae, has been consistently disregarded.

Multiple mechanisms of action for inhibitors of histidine protein kinases from bacterial two-component systems

Many pathogenic bacteria utilize two-component systems consisting of a histidine protein kinase (HPK) and a response regulator (RR) for signal transduction. During the search for novel inhibitors, several chemical series, including benzoxazines, benzimidazoles, bis-phenols, cyclohexenes, trityls, and salicylanilides, were identified that inhibited the purified HPK-RR pairs KinA-Spo0F and NRII-NRI, with 50% inhibitory concentrations (IC50s) ranging from 1.9 to >500 microM and MICs ranging from 0.5 to >16 microg/ml for gram-positive bacteria. However, additional observations suggested that mechanisms other than HPK inhibition might contribute to antibacterial activity. In the present work, representative compounds from the six different series of inhibitors were analyzed for their effects on membrane integrity and macromolecular synthesis. At 4x MIC, 17 of 24 compounds compromised the integrity of the bacterial cell membrane within 10 min, as measured by uptake of propidium iodide. In this set, compounds with lower IC50s tended to cause greater membrane disruption. Eleven of 12 compounds inhibited cellular incorporation of radiolabeled thymidine and uridine >97% in 5 min and amino acids >80% in 15 min. The HPK inhibitor that allowed >25% precursor incorporation had no measurable MIC (>16 microg/ml). Fifteen of 24 compounds also caused hemolysis of equine erythrocytes. Thus, the antibacterial HPK inhibitors caused a rapid decrease in cellular incorporation of RNA, DNA, and protein precursors, possibly as a result of the concomitant disruption of the cytoplasmic membrane. Bacterial killing by these HPK inhibitors may therefore be due to multiple mechanisms, independent of HPK inhibition.

Killing of endothelial cells and release of arachidonic acid. Synergistic effects among hydrogen peroxide, membrane-damaging agents, cationic substances, and proteinases and their modulation by inhibitors

51Chromium-labeled rat pulmonary artery endothelial cells (EC) cultivated in MEM medium were killed, in a synergistic manner, by mixtures of subtoxic amounts of glucose oxidase-generated H2O2 and subtoxic amounts of the following agents: the cationic substances, nuclear histone, defensins, lysozyme, poly-L-arginine, spermine, pancreatic ribonuclease, polymyxin B, chlorhexidine, cetyltrimethyl ammonium bromide, as well as by the membrane-damaging agents phospholipases A2 (PLA2) and C (PLC), lysolecithin (LL), and by streptolysin S (SLS) of group A streptococci. Cytotoxicity induced by such mixtures was further enhanced by subtoxic amounts either of trypsin or of elastase. Glucose-oxidase cationized by complexing to poly-L-histidine proved an excellent deliverer of membrane-directed H2O2 capable of enhancing EC killing by other agonists. EC treated with rabbit anti-streptococcal IgG were also killed, in a synergistic manner, by H2O2, suggesting the presence in the IgG preparation of cross-reactive antibodies. Killing of EC by the various mixtures of agonists was strongly inhibited by scavengers of hydrogen peroxide (catalase, dimethylthiourea, MnCl2), by soybean trypsin inhibitor, by polyanions, as well as by putative inhibitors of phospholipases. Strong inhibition of cell killing was also observed with tannic acid and by extracts of tea, but less so by serum. On the other hand, neither deferoxamine, HClO, TNF, nor GTP gamma S had any modulating effects on the synergistic cell killing. EC exposed either to 6-deoxyglucose, puromycin, or triflupromazin became highly susceptible to killing by mixtures of hydrogen peroxide with several of the membrane-damaging agents. While maximal synergistic EC killing was achieved by mixtures of H2O2 with either PLA2, PLC, LL, or with SLS, a very substantial release of [3H]arachidonic acid (AA), PGE2, and 6-keto-PGF occurred only if a proteinase was also added to the mixture of agonists. The release of AA from EC was markedly inhibited either by scavengers of H2O2, by proteinase inhibitors, by cationic agents, by HClO, by tannic acid, and by quinacrin. We suggest that cellular injury induced in inflammatory and infectious sites might be the result of synergistic effects among leukocyte-derived oxidants, lysosomal hydrolases, cytotoxic cationic polypeptides, proteinases, and microbial toxins, which might be present in exudates. These "cocktails" not only kill cells, but also solubilize AA and several of its metabolites. However, AA release by the various agonists can be also achieved following attack by leukocyte-derived agonists on dead cells. It is proposed that treatment by "cocktails" of adequate antagonists might be beneficial to protect against cellular injury in vivo.

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.

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)

Comparison of in vivo degradation of 125I-labeled peptidoglycan-polysaccharide fragments from group A and group D streptococci

The in vivo degradation and persistence of 125I-labeled peptidoglycan-polysaccharide (PG-PS) fragments from the cell walls of group A and D streptococci were compared by group after intraperitoneal injection into rats. The quantity of PG-PS in the livers and spleens of group D PG-PS-injected rats was less than the quantity in rats injected with group A PG-PS throughout the course of the experiment. Gel filtration analyses of liver and spleen homogenates indicated that group A PG-PS was relatively resistant to degradation, whereas group D PG-PS was extensively degraded to yield a heterogeneous mixture of fragments of lower molecular weight. There was no significant difference in the content of group A PG-PS versus that of group D in joints or blood samples. Analysis of fragment sizes in these tissues also indicated more extensive degradation of group D PG-PS. However, the majority of group A PG-PS in blood samples and joints was a lower molecular weight than that found in the livers or spleens. We conclude that group A PG-PS undergoes a significant but low level of degradation and that group D PG-PS is much less persistent and more extensively degraded than group A PG-PS is in vivo. These differences in PG-PS catabolism may account, in part, for the capacity of group A PG-PS to induce chronic, recurrent arthritis of longer duration than that induced by group D PG-PS.

In vitro and in vivo effect of immunoglobulin G on the integrity of bacterial membranes

The interaction between a modified 7S immunoglobulin (MISG) and bacterial membranes was studied by adopting in vitro as well as in vivo techniques. Preincubation of Escherichia coli and Pseudomonas aeruginosa with MISG resulted in a release of enzymatic markers from the periplasmic space, whereas no cytoplasmic or membrane-bound enzymes were liberated. Due to the interaction of MISG with the outer membrane of gram-negative rods, the bacteria became more susceptible to the antibacterial action of poorly penetrating penicillins because of a significantly increased rate of uptake. These in vitro effects were corroborated under in vivo conditions by adopting the granuloma pouch model. A single intravenous injection of MISG enhanced the therapeutic efficacy of mezlocillin against E. coli; similarly, the antibacterial activity of penicillin G, oxacillin, cephalothin and cefamandole against Staphylococcus aureus was augmented by MISG. These in vivo effects of MISG were not due to an increased rate of phagocytosis or complement activity. Thus, MISG sensitized bacteria to several beta-lactam antibiotics by disorganizing their outer membrane.

Bacteria and zymosan opsonized with histone, dextran sulfate, and polyanetholesulfonate trigger intense chemiluminescence in human blood leukocytes and platelets and in mouse macrophages: modulation by metabolic inhibitors in relation to leukocyte-bacteria interactions in inflammatory sites

Human blood leukocytes and platelets and mouse peritoneal macrophages emit very rapid and very intense Luminol-dependent chemiluminescence (CL) signals when treated with streptococci, staphylococci, or with zymosan, which have been preopsonized with arginine-rich histone, dextran sulfate or polyanetholesulfonate (liquoid). Liquoid alone at 10-30 micrograms/2 X 10(5) leukocytes also triggers intense CL responses in the absence of a carrier. Strong CL can also be triggered, and at the same levels, when the various polyelectrolytes are simply mixed with the bacteria or zymosan and added to the leukocyte suspensions. The CL responses induced by the polyelectrolyte-bacteria complexes greatly exceed those triggered in leukocytes by antibody-complement-coated particles. Liquoid also shows a unique property of markedly augmenting CL signals which have already been induced by other ligand-coated bacteria or zymosan particles. Streptococci and staphylococci were found to be much superior to zymosan, Gram-positive bacilli, or E. coli as carriers for the various polyelectrolytes in the CL reaction. Neither protamine sulfate, lysozyme, myeloperoxidase, crystalline ribonuclease (all cationic in nature), chondroitin sulfate, heparin, nor alginate sulfate acted as ligands for triggering CL, when used to opsonize bacteria or zymosan. The induction of CL in blood leukocytes by the various ligand-coated bacteria is markedly inhibited by azide, KCN catalase, aminotriazole, and EDTA, agents known to inhibit the production of oxygen radicals following stimulation of leukocytes by opsonized bacteria. Two children diagnosed for chronic granulomatous diseases (CGD) of childhood and an apparently healthy sister of one of the male patients completely failed to respond with CL either to the polyelectrolyte-bacteria complexes, liquoid or antibody-coated bacteria and zymosan. It is proposed that liquoid be employed for the rapid screening of defects in certain oxygen-dependent metabolic processes in both PMNs and macrophages. It is also suggested that polyelectrolytes like the ones described in this study may markedly enhance the bactericidal properties of leukocytes and macrophages towards both extracellular and intracellular microorganisms and may perhaps also augment the tumoricidal effects of activated macrophages.