Bactericidal/permeability increasing protein and host defense against gram-negative bacteria and endotoxin

Salivary bactericidal/permeability-increasing protein: A novel inflammatory marker associated with periodontitis

OBJECTIVES

The present case-control study aims to investigate the salivary levels of bactericidal/permeability-increasing protein (BPI) and interleukin-1beta (IL-1ß) in systemically healthy individuals with periodontitis and periodontally healthy for the evaluation of BPI's relation with periodontal inflammation and clinical diagnosis of periodontitis.

MATERIALS AND METHODS

A total of 100 participants were enrolled in this study and divided into periodontitis (P group) (n = 50) and periodontally healthy (H group) (n = 50) groups based on their full-mouth periodontal examination results including plaque index, probing pocket depth, gingival index, bleeding on probing, and clinical attachment level. Unstimulated whole saliva was collected. Salivary BPI and IL-1β levels were determined using an enzyme-linked immunosorbent assay. Receiver operating characteristic (ROC) curves were created to determine the diagnostic value of BPI.

RESULTS

The levels of BPI and IL-1ß in saliva were significantly higher in the P group than in the H group (p<0.001). Moreover, salivary BPI and IL-1ß levels correlated significantly with all clinical periodontal parameters (all p<0.001). Interestingly, there was a strong positive correlation between salivary levels of BPI and IL-1ß (r=0.544, p<0.001). In addition, the results of the ROC curve analysis showed that BPI had a high diagnostic potential to distinguish periodontitis from healthy controls with an area under the curve value of 0.94% (p<0.000).

CONCLUSION

The significantly higher salivary levels of BPI in periodontitis patients together with strong positive correlations between all periodontal parameters and salivary IL-1ß levels suggest that BPI may be involved in the inflammatory process of periodontal disease.

CLINICAL RELEVANCE

The present study for the first time report that salivary BPI levels may serve as a potential biomarker of inflammation in periodontal disease.

TRIAL REGISTRATION NUMBER

Thai Clinical Trials.gov (TCTR20211222008) (22 December 2021).

The potential of AFM in studying the role of the nanoscale amphipathic nature of (lipo)-peptides interacting with lipid bilayers

Antimicrobial peptides (AMPs) and lipopeptides (LPs) represent very promising molecules to fight resistant bacterial infections due to their broad-spectrum of activity, their first target, i.e. the bacterial membrane, and the rapid bactericidal action. For both types of molecules, the action mechanism starts from the membrane of the pathogen agents, producing a disorganization of their phase structure or the formation of pores of different size altering their permeability. This mechanism of action is based on physical interactions more than on a lock-and-key recognition event and it is difficult for the pathogens to rapidly develop an effective resistance. Very small differences in the sequence of both AMPs and LPs might lead to very different effects on the target membrane. Therefore, a correct understanding of their mechanism of action is required with the aim of developing new synthetic peptides, analogues of the natural ones, with specific and more powerful bactericidal activity. Atomic force microscopy (AFM), with its high resolution and the associated force spectroscopy resource, provides a valuable technique to investigate the reorganization of lipid bilayers exposed to antimicrobial or lipopeptides. Here, we present AFM results obtained by ours and other groups on the action of AMPs and LPs on supported lipid bilayers (SLBs) of different composition. We also consider data obtained by fluorescence microscopy to compare the AFM data with another technique which can be used on different lipid bilayer model systems such as SLBs and giant unilamellar vesicles. The outcomes here presented highlight the powerful of AFM-based techniques in detecting nanoscale peptide-membrane interactions and strengthen their use as an exceptional complementary tool toin vivoinvestigations. Indeed, the combination of these approaches can help decipher the mechanisms of action of different antimicrobials and lipopeptides at both the micro and nanoscale levels, and to design new and more efficient antimicrobial compounds.

DAPTOMYCIN, its membrane-active mechanism vs. that of other antimicrobial peptides

Over 3000 membrane-active antimicrobial peptides (AMPs) have been discovered, but only three of them have been approved by the U.S. Food and Drug Administration (FDA) for therapeutic applications, i.e., gramicidin, daptomycin and colistin. Of the three approved AMPs, daptomycin is a last-line-of-defense antibiotic for treating Gram-positive infections. However its use has already created bacterial resistance. To search for its substitutes that might counter the resistance, we need to understand its molecular mechanism. The mode of action of daptomycin appears to be causing bacterial membrane depolarization through ion leakage. Daptomycin forms a unique complex with calcium ions and phosphatidylglycerol molecules in membrane at a specific stoichiometric ratio: Dap₂Ca₃PG₂. How does this complex promote ion conduction across the membrane? We hope that biophysics of peptide-membrane interaction can answer this question. This review summarizes the biophysical works that have been done on membrane-active AMPs to understand their mechanisms of action, including gramicidin, daptomycin, and underdeveloped pore-forming AMPs. The analysis suggests that daptomycin forms transient ionophores in the target membranes. We discuss questions that remain to be answered.

rBPI21 (Opebacan) Promotes Rapid Trilineage Hematopoietic Recovery in a Murine Model of High-Dose Total Body Irradiation

The complexity of providing adequate care after radiation exposure has drawn increasing attention. While most therapeutic development has focused on improving survival at lethal radiation doses, acute hematopoietic syndrome (AHS) occurs at substantially lower exposures. Thus, it is likely that a large proportion of such a radiation-exposed population will manifest AHS of variable degree and that the medical and socioeconomic costs of AHS will accrue. Here, we examined the potential of rBPI21 (opebacan), used without supportive care, to accelerate hematopoietic recovery after radiation where expected survival was substantial (42-75%) at 30 days). rBPI21 administration was associated with accelerated recovery of hematopoietic precursors and normal marrow cellularity, with increases in megakaryocyte numbers particularly marked. This translated into attaining normal trilineage peripheral blood counts 2-3 weeks earlier than controls. Elevations of hematopoietic growth factors observed in plasma and the marrow microenvironment suggest the mechanism is likely multifactorial and not confined to known endotoxin-neutralizing and cytokine down-modulating activities of rBPI21 . These observations deserve further exploration in radiation models and other settings where inadequate hematopoiesis is a prominent feature. These experiments also model the potential of therapeutics to limit the allocation of scarce resources after catastrophic exposures as an endpoint independent of lethality mitigation. This article is protected by copyright. All rights reserved.

Understanding membrane-active antimicrobial peptides

Bacterial membranes represent an attractive target for the design of new antibiotics to combat widespread bacterial resistance to traditional inhibitor-based antibiotics. Understanding how antimicrobial peptides (AMPs) and other membrane-active agents attack membranes could facilitate the design of new, effective antimicrobials. AMPs, which are small, gene-encoded host defense proteins, offer a promising basis for the study of membrane-active antimicrobial agents. These peptides are cationic and amphipathic, spontaneously binding to bacterial membranes and inducing transmembrane permeability to small molecules. Yet there are often confusions surrounding the details of the molecular mechanisms of AMPs. Following the doctrine of structure-function relationship, AMPs are often viewed as the molecular scaffolding of pores in membranes. Instead we believe that the full mechanism of AMPs is understandable if we consider the interactions of AMPs with the whole membrane domain, where interactions induce structural transformations of the entire membrane, rather than forming localized molecular structures. We believe that it is necessary to consider the entire soft matter peptide-membrane system as it evolves through several distinct states. Accordingly, we have developed experimental techniques to investigate the state and structure of the membrane as a function of the bound peptide to lipid ratio, exactly as AMPs in solution progressively bind to the membrane and induce structural changes to the entire system. The results from these studies suggest that global interactions of AMPs with the membrane domain are of fundamental importance to understanding the antimicrobial mechanisms of AMPs.

Antimicrobial and Antibiofilm Effects of Human Amniotic/Chorionic Membrane Extract on Streptococcus pneumoniae

Background:Streptococcus pneumoniae colonize the human nasopharynx in the form of biofilms. The biofilms act as bacterial reservoirs and planktonic bacteria from these biofilms can migrate to other sterile anatomical sites to cause pneumonia, otitis media (OM), bacteremia and meningitis. Human amniotic membrane contains numerous growth factors and antimicrobial activity; however, these have not been studied in detail. In this study, we prepared amniotic membrane extract and chorionic membrane extract (AME/CME) and evaluated their antibacterial and antibiofilm activities against S. pneumoniae using an in vitro biofilm model and in vivo OM rat model.

Materials and Methods: The AME/CME were prepared and protein was quantified using DC^TM (detergent compatible) method. The minimum inhibitory concentrations were determined using broth dilution method, and the synergistic effect of AME/CME with Penicillin-streptomycin was detected checkerboard. The in vitro biofilm and in vivo colonization of S. pneumoniae were studied using microtiter plate assay and OM rat model, respectively. The AME/CME-treated biofilms were examined using scanning electron microscope and confocal microscopy. To examine the constituents of AME/CME, we determined the proteins and peptides of AME/CME using tandem mass tag-based quantitative mass spectrometry.

Results: AME/CME treatment significantly (p < 0.05) inhibited S. pneumoniae growth in planktonic form and in biofilms. Combined application of AME/CME and Penicillin-streptomycin solution had a synergistic effect against S. pneumoniae. Biofilms grown with AME/CME were thin, scattered, and unorganized. AME/CME effectively eradicated pre-established pneumococci biofilms and has a bactericidal effect. AME treatment significantly (p < 0.05) reduced bacterial colonization in the rat middle ear. The proteomics analysis revealed that the AME/CME contains hydrolase, ribonuclease, protease, and other antimicrobial proteins and peptides.

Conclusion: AME/CME inhibits S. pneumoniae growth in the planktonic and biofilm states via its antimicrobial proteins and peptides. AME/CME are non-cytotoxic, natural human product; therefore, they may be used alone or with antibiotics to treat S. pneumoniae infections.

Mode of Action of Antimicrobial Peptides on E. coli Spheroplasts

We investigated the phenomena of antimicrobial peptides (AMPs) directly attacking the cytoplasmic membranes of Escherichia coli spheroplasts. We developed a procedure for fluorescence recovery after photobleaching to examine dye leakage through bacterial membranes as AMPs in solution bound to the membranes. We found that the AMP binding did not increase the apparent membrane area of a spheroplast, contrary to the response of a lipid-bilayer vesicle, which always showed a membrane area expansion by AMP binding. The permeability through the bacterial membrane increased in a sigmoidal fashion as the AMP binding increased in time, exhibiting a cooperative behavior of AMPs. The analysis of fluorescence recovery after photobleaching showed that the fluxes of dye molecules into and out of the cell were consistent with diffusion of molecules through a number of pores that increased with binding of AMPs and then saturated to a steady level. We discovered a new, to our knowledge, experimental parameter called the flux rate that characterizes the AMP-induced permeability of dye molecules through bacterial membranes. The phenomena observed in bacterial membranes are consistent with the pore-forming activities of AMPs previously observed in lipid bilayers. The experimental value of the flux rate per pore is much smaller than a theoretical value that assumes no friction for the dye molecule's permeation through the pore. We believe that experimental studies of the flux rate will be useful for further analysis of AMPs' permeabilization mechanisms.

Yeast recombinant Factor C from horseshoe crab binds endotoxin and causes bacteriostasis

Carcinoscorpius rotundicauda Factor C cDNA has been cloned and expressed in Pichia pastoris to produce a recombinant full-length Factor C (rFC) which is both immunoreactive and functional. The presence of a functional endotoxin-binding domain on rFC was ascertained by LPS-binding assays. One involved the relative binding affinity of rFC to electroblotted lipid A moiety of LPS. The second assay showed that rFC competed against native Factor C contained in C. rotundicauda amebocyte lysate (CAL) to bind LPS. Purification of rFC enhanced its binding affinity to LPS. By agglutination, rFC caused bacteriostasis of Gram-negative bacteria within 2 h. In an in vivo system, rFC also decreased the mortality of actinomycin D-sensitized/LPS-challenged mice. The rFCEE, bearing the 5' terminal LPS binding domain displayed a lowered affinity for LPS. This is in contrast to the rFCSN subclone that is devoid of the 5' end of Factor C, and which does not bind LPS. The presence of a fully-functional endotoxin binding domain in rFC probably requires a full-length protein for co-operative interaction of its downstream sequences. Thus, rFC has potential in the detection and removal of contaminating LPS from biological specimens and fluids for injection, since it is capable of binding both free and bound lipid A.

Review: Bacterial endotoxin and the human monoclonal antibody HA-IA: specificity, potential mechanisms of action, and limits to its effectiveness

Bacterial endotoxins are lipopolysaccharides present in the outer membrane of all Gram-negative bacteria (GNB). Endotoxins consist of a lipid moiety, lipid A, that is covalently linked to highly variable, serotype O-specific polysaccharide lateral chains. In contrast, the endotoxin core, which includes lipid A, is better conserved and can be recognized by antibodies showing cross-reactivity among various GNB. Such polyclonal and monoclonal antibodies have been developed in an attempt to neutralize the biological and dele. terious effects of endotoxin, thus preventing lipid A from binding to macrophages. In fact, almost all the biological activities of endotoxin are elicited by lipid A, and there is substantial evidence to the effect that the monocyte-macrophage is the principal mediator of endotoxicity. Antiserum against LPS isolated from rough mutants of GNB (expressing virtually only the central core-lipid A), has been shown to counteract the lethal effects of endotoxin in animals and humans. However, such serum or plasma contains antibodies of different specificities and isotypes which represent different effector functions, insofar as LPS is a very complex and highly heterogenous macromolecule. Because of the difficulties encountered in investigating the nature and specificity of the protection afforded by these antisera, and their limited capacity of production for therapeutic use, specific anti-lipid A monoclonal antibodies have been produced in their stead. A variety of mouse and human monoclonal antibodies against LPS have been generated and selected for their ability to cross-react with many GNB species. The most recent clinical trials involving the treatment of septic patients with human HA-IA (Centoxin) or with murine (E5) anti-lipid A monoclonal antibody showed no difference in survival rates, as compared to treatment with a placebo. However, statistical significance was demonstrated in subsets of patients suffering from documented Gram-negative septicemia or Gram-negative sepsis without refractory shock. The usefulness of anti-lipid A antibodies will undoubtedly remain controversial, since they appear to benefit only a minority of all patients treated, and also because no consensus exists regarding their specificity and modes of action. The aim of this review is to describe results which demonstrate the requirements for, difficulties in and limits to, elucidating the ability of certain antibodies to recognize structural elements present in the lipid A domain of LPS. A clear demonstration of antibody cross-reactivity was obtained only when rough LPS bacteria were used, and was markedly enhanced when smooth bacteria had been pretreated with cell wall active antibiotics. Further, new data have recently demonstrated the specific involvement of HA-IA in the immunocytoadherence assay in the presence of human complement and human red blood cells. Such phenomena may form part of the potential role for natural or monoclonal human IgM anti-lipid A antibodies, which will be to remove IgM-lipid A immune complexes through transhepatic clearance via C3b binding to the CR1 present on circulating human erythrocytes. Insofar as immunocytoadherence is a multiparameter phenomenon, various limiting factors probably interfere with its mechanism of clearance. These factors may be absent in various subsets of septic patients under treatment, thus explaining therapeutic failures with HA-IA in humans or preclinical animal studies. Several clinical settings involving defects to CR1 expression, C3b production, LPS recognition and hepatic clearance dysfunction are described. Long term, however, it will impossible to specify the patient subsets suitable for monoclonal therapy without first defining their characteristics. HA-IA may be able to inhibit one of the earliest stages in activation of the cytokine cascade by sequestrating and eliminating biologically active lipid A. The major problem today in terms of using anti-lipid A antibodies is an efficiently early detection of specific pathway defects which detract from or nullify the HA-IA therapeutic effect.

rBPI(10—193) is secreted by CHO cells and retains the activity of rBPI21

rBPI23, a recombinant N-terminal fragment of human bactericidal/permeability-increasing protein (BPI), kills Gram-negative bacteria and neutralizes endotoxin. rBPI 21, a variant in which cysteine 132 is changed to alanine, retains the activities of rBPI23. Analysis of certain purified rBPI 21 preparations revealed that some of the molecules had lost nine amino acids from the amino terminus. To explore the effect of this modification on structure and activity, we cloned and expressed a variant of rBPI 21, designated rBPI(10-193), which lacks the first nine amino acids. A monoclonal antibody believed to recognize the amino terminus of rBPI 21 cross-reacted with rBPI21, but not with rBPI(10-193) or full length recombinant BPI (rBPI). These results demonstrated that the antibody recognizes the first nine amino acids of rBPI21 and that this region of the holoprotein (rBPI) is inaccessible to the antibody (as suggested by the known 3-D structure). Purified rBPI(10193) and rBPI 21 were similarly potent in in vitro assays measuring bactericidal, endotoxin binding and neutralization activities. In a mouse model of lethal bacteremia, rBPI(10-193) and rBPI21 were similarly potent whereas in a mouse endotoxin challenge model, rBPI(10-193) appeared to be at least 2-fold more potent than rBPI21. In conscious rats, a rapid bolus dose of 40 mg/kg of rBPI21 caused a significant transient decrease in blood pressure while the same dose of rBPI(10-193) caused no blood pressure decrease. We conclude from these studies that the first nine amino acids of rBPI21 are not essential for the anti-infective and endotoxin-neutralizing activities of BPI.

Neutrophil-derived Oxidants and Proteinases as Immunomodulatory Mediators in Inflammation

Neutrophils generate potent microbicidal molecules via the oxygen-dependent pathway, leading to the generation of reactive oxygen intermediates (ROI), and via the non-oxygen dependent pathway, consisting in the release of serine proteinases and metalloproteinases stored in granules. Over the past years, the concept has emerged that both ROI and proteinases can be viewed as mediators able to modulate neutrophil responses as well as the whole inflammatory process. This is well illustrated by the oxidative regulation of proteinase activity showing that oxidants and proteinases acts is concert to optimize the microbicidal activity and to damage host tissues. ROI and proteinases can modify the activity of several proteins involved in the control of inflammatory process. Among them, tumour necrosis factor-α and interleukin-8, are elective targets for such a modulation. Moreover, ROI and proteinases are also able to modulate the adhesion process of neutrophils to endothelial cells, which is a critical step in the inflammatory process.

Deficient expression of bactericidal/permeability-increasing protein in immunocompromised hosts: translational potential of replacement therapy

BPI (bactericidal/permeability-increasing protein) is a 55 kDa anti-infective molecule expressed in neutrophil and eosinophil granules and on some epithelial cells. BPI's high affinity for the lipid A region of endotoxin targets its opsonizing, microbicidal and endotoxin-neutralizing activities towards Gram-negative bacteria. Several immunocompromised patient populations demonstrate BPI deficiency, including newborns, those with anti-neutrophil cytoplasmic antibodies (as in cystic fibrosis and HIV infection) and those exposed to radiochemotherapy. BPI may be replenished by administering agents that induce its expression or by administration of recombinant BPI congeners, potentially shielding BPI-deficient individuals against Gram-negative bacterial infection, endotoxemia and its toxic sequelae.

Soluble MD-2 is an acute-phase protein and an opsonin for Gram-negative bacteria

Myeloid differentiation factor-2 (MD-2) is a lipopolysaccharide (LPS)-binding protein usually coexpressed with and binding to Toll-like receptor 4 (TLR4), conferring LPS responsiveness of immune cells. MD-2 is also found as a soluble protein. Soluble MD-2 (sMD-2) levels are markedly elevated in plasma from patients with severe infections, and in other fluids from inflamed tissues. We show that sMD-2 is a type II acute-phase protein. Soluble MD-2 mRNA and protein levels are up-regulated in mouse liver after the induction of an acute-phase response. It is secreted by human hepatocytic cells and up-regulated by interleukin-6. Soluble MD-2 binds to Gram-negative but not Gram-positive bacteria, and sMD-2 secreted by hepatocytic cells is an essential cofactor for the activation of TLR4-expressing cells by Gram-negative bacteria. Soluble MD-2 opsonization of Gram-negative bacteria accelerates and enhances phagocytosis, principally by polymorphonuclear neutrophils. In summary, our results demonstrate that sMD-2 is a newly recognized type II acute-phase reactant, an opsonin for Gram-negative bacteria, and a cofactor essential for the activation of TLR4-expressing cells. This suggests that sMD-2 plays a key role in the host innate immune response to Gram-negative infections.

Bactericidal permeability-increasing protein in host defence against gram-negative bacteria and endotoxin

The bactericidal permeability-increasing protein (BPI) is a highly conserved host-defence molecule produced and stored by myeloid cells only and a major constituent of the primary granules of human and rabbit polymorphonuclear leukocytes. The c. 50 kDa BPI and a c. 23 kDa bioactive N-terminal fragment are cytotoxic only for Gram-negative bacteria. This target-cell specificity reflects the high affinity (apparent Kd: 1-10 nM) of BPI for the lipid A portion of lipopolysaccharide (LPS or endotoxin). Native and recombinant (r) holo-BPI and the N-terminal fragment (rBPI-23) bind with equal affinity to all forms of isolated LPS examined and inhibit the numerous biological effects of LPS in vitro (including in whole blood ex vivo) as well as in animals. Under the same conditions the antibacterial potencies of holo-BPI and rBPI-23 against Gram-negative bacteria with rough chemotype LPS (whether encapsulated or not) are also the same, but against more resistant smooth chemotype Gram-negative bacteria rBPI-23 is up to 30-fold more potent than holo-BPI. Holo-BPI and rBPI-23 protect a broad range of animals against lethal cytotoxic effects of LPS and in some cases against lethal inoculations with live Gram-negative bacteria.

Gene-encoded antibiotics made in bacteria

Production of antimicrobial peptides and proteins is very common among bacteria and a variety of such substances has been described. In general Gram-negative bacteria produce protein bacteriocins (e.g. colicins) with narrow action spectra based on receptor-mediated activity. They produce comparatively few peptides, such as the post-translationally modified microcin B17. In contrast Gram-positive bacteria tend to produce peptide bacteriocins smaller than 10 kDa and of wider activity spectra. These show particular potential for application. They can be divided into unmodified peptides (e.g. lactococcins, lactacins, pediocins) and lanthionine-containing peptides (lantibiotics, e.g. nisin, epidermin, Pep5). The unmodified peptides are mostly hydrophobic or amphiphilic and act by disturbing the function of the cytoplasmic membrane. They are synthesized as prepeptides with a characteristic N-terminal leader peptide. In some cases genes for immunity peptides were found in close proximity to structural genes; furthermore, two-component response regulators seem to be involved in the regulation of their synthesis. The biosynthetic genes for lantibiotics are also organized in operons. Lantibiotic gene clusters include genes encoding the unique enzymes which dehydrate serine and threonine and form the characteristic thioether-bridged lanthionines. Three types of lantibiotics are currently distinguished on the basis of structural features and functional aspects: type A, which include elongated, amphiphilic, pore-forming peptides (e.g. nisin); type B, which are of globular shape and inhibit phospholipases (e.g. duramycins); and type C (e.g. actagardine) with intermediate features which act by inhibiting bacterial cell wall biosynthesis.

Endotoxin-induced expression of murine bactericidal permeability/increasing protein is mediated exclusively by toll/IL-1 receptor domain-containing adaptor inducing IFN-beta-dependent pathways

Antimicrobial effector proteins are a key mechanism for the innate immune system to combat pathogens once they infect the host. We report the identification and cloning of the mouse homologue of human bactericidal permeability/increasing protein (BPI). Mouse BPI is constitutively expressed in lymphatic organs and tissues as well as in mouse testis. Upon stimulation with different TLR ligands, mouse BPI is strongly expressed in granulocytes and, surprisingly, in bone marrow-derived dendritic cells. Mouse BPI is most strongly induced by bacterial LPS through a signaling pathway that is completely dependent on TLR4-Toll/IL-1R domain-containing adaptor inducing IFN-beta. Functional studies revealed that mouse BPI does have the potential to neutralize LPS and inhibits bacterial growth. Mouse BPI is expressed in granulocytes and bone marrow-derived dendritic cells, and the transcriptional activation is controlled by TLRs.

Endotoxin recognition: in fish or not in fish?

The interaction between pathogens and their multicellular hosts is initiated by activation of pathogen recognition receptors (PRRs). These receptors, that include most notably members of the toll-like receptor (TLR) family, recognize specific pathogen-associated molecular patterns (PAMPs). TLR4 is a central part of the receptor complex that is involved in the activation of the immune system by lipopolysaccharide (LPS) through the specific recognition of its endotoxic moiety (Lipid A). This is a critical event that is essential for the immune response to Gram-negative bacteria as well as the etiology of endotoxic shock. Interestingly, compared to mammals, fish are resistant to endotoxic shock. This in vivo resistance concurs with in vitro studies demonstrating significantly lowered sensitivity of fish leukocytes to LPS activation. Further, our in vitro analyses demonstrate that in trout mononuclear phagocytes, LPS fails to induce antiviral genes, an event that occurs downstream of TLR4 and is required for the development of endotoxic shock. Finally, an in silico approach that includes mining of different piscine genomic and EST databases, reveals the presence in fish of all of the major TLR signaling elements except for the molecules specifically involved in TLR4-mediated endotoxin recognition and signaling in mammals. Collectively, our analysis questions the existence of TLR4-mediated cellular responses to LPS in fish. We further speculate that other receptors, in particular beta-2 integrins, may play a primary role in the activation of piscine leukocytes by LPS.

Polymyxin B: an ode to an old antidote for endotoxic shock

Endotoxic shock, a syndrome characterized by deranged hemodynamics, coagulation abnormalities, and multiple system organ failure is caused by the release into the circulation of lipopolysaccharide (LPS), the structurally diverse component of Gram-negative bacterial outer membranes, and is responsible for 60% mortality in humans. Polymyxin B (PMB), a cyclic, cationic peptide antibiotic, neutralizes endotoxin but induces severe side effects in the process. The potent endotoxin neutralizing ability of PMB, however, offers possibilities for designing non-toxic therapeutic agents for combating endotoxicosis. Amongst the numerous approaches for combating endotoxic shock, peptide mediated neutralization of LPS seems to be the most attractive one. The precise mode of binding of PMB to LPS and the structural features involved therein have been elucidated only recently using a variety of biophysical approaches. These suggest that efficient neutralization of endotoxin by PMB is not achieved by mere binding to LPS but requires its sequestration from the membrane. Incorporation of this feature into the design of endotoxin neutralizing peptides should lead to the development of effective antidotes for endotoxic shock.

The role of tumour necrosis factor in the kinetics of lipopolysaccharide-mediated neutrophil priming in whole blood

Neutrophils can be primed by bacterial lipopolysaccharide (LPS) for an enhanced oxidative burst, which is a key element in the pathogenesis of Gram-negative sepsis. Some serum proteins (e.g. lipopolysaccharide-binding protein) avidly bind LPS and markedly enhance receptor binding and cellular activation while other serum factors (lipoproteins, bactericidal/permeability-increasing protein) neutralize LPS and prevent neutrophil activation. In this paper we examined the kinetics of this priming reaction in whole blood. To study the balance between neutrophil activation and LPS neutralization a sensitive chemiluminescence assay was used in a whole blood system. LPS was able to prime neutrophils for enhanced oxidative burst in whole blood with an optimum incubation time of 25 min. However, LPS was neutralized very rapidly with a t(1/2) of 10 min. After 20 min a second priming factor was already generated, which was shown to be monocyte-derived tumour necrosis factor (TNF).

Activation of rainbow trout (Oncorhynchus mykiss) mononuclear phagocytes by different pathogen associated molecular pattern (PAMP) bearing agents

Rainbow trout (Oncorhynchus mykiss) cells of a monocyte-macrophage lineage (rtMOCs) were used to characterize the ability of the trout innate immune system to recognize and respond to different pathogen associated molecular pattern (PAMP) bearing substances. Compared to what has been reported for mammalian macrophages, rtMOCs responded with lower sensitivity to lipopolysaccharide (LPS) from Escherichia coli (EC-LPS) and Pseudomonas aeruginosa (PA-LPS). The sensitivity of rtMOCs to LPS was not influenced by the presence of serum which suggests that the resistance to endotoxic shock in fish may be due to the lack of serum-borne factors that confer sensitivity to LPS in mammals. The time course of the response to PAMPs could be separated into two patterns. EC-LPS induced stable cytokine expression whereas PA-LPS, zymosan and muramyl dipeptide induced transient TNF2 expression. By analogy to the type of stimulation observed in mammals it can be hypothesized that different signaling pathways, possibly initiated by different receptors, may be involved in the recognition of these PAMPs by rtMOCs.

Proteolytic fragments of ovalbumin display antimicrobial activity

Ovalbumin, one of the major proteins present in avian egg white, was proteolytically digested by trypsin and chymotrypsin and the peptide fragments were investigated for their antimicrobial activity. The antimicrobial peptides were isolated and characterized. From the tryptic digestion, the following five antimicrobial peptide fragments were obtained: SALAM (residues 36-40), SALAMVY (residues 36-42) YPILPEYLQ (residues 111-119), ELINSW (residues 143-148) and NVLQPSS (residues 159-165). Digestion of ovalbumin by chymotrypsin yielded the antimicrobial peptides AEERYPILPEYL (residues 127-138), GIIRN (residues 155-159) and TSSNVMEER (residues 268-276). The peptides were synthesized and found to exert antimicrobial activity. They were strongly active against Bacillus subtilis and to a lesser extent against the other bacterial strains examined. A weak fungicidal activity against Candida albicans was also shown by some peptides. Ovalbumin itself was not bactericidal against all the bacteria strains examined. Our results suggest that the food protein ovalbumin may supply the organism with antimicrobial peptides, supporting the immunodefences of the organism.

Biopanning of endotoxin-specific phage displayed peptides

Systemic bacterial infections frequently lead to a plethora of symptoms termed "endotoxic shock" or "sepsis." Characterized by hypotension, coagulation abnormalities, and multiple organ failure, treatment of sepsis still remains mostly supportive. Of the various experimental therapeutic interventional strategies, neutralization of endotoxin by peptides or proteins is becoming popular recently. Hence, design of endotoxin binding peptides is gaining currency as their structural complexity and mode of recognition of endotoxin precludes mounting of resistance against them by the susceptible bacteria by genetic recombination, mutation, etc. Earlier work from our laboratory had shown that the amphiphilic cationic peptides are good ligands for endotoxin binding. In this study, we report the results of studies with the 12 selected lipid A binding phage displayed peptides by biopanning of a repertoire of a random pentadecapeptide library displayed on the filamentous M-13 phage. A comparison of the sequences revealed no consensus sequence between the 12 selected peptides suggesting that the lipid A binding motif is not sequence specific which is in accord with the sequence variation seen with the naturally occurring anti-microbial and/or endotoxin binding peptides. Thus, the flexibility of the peptides coupled with their plasticity in recognizing the lipid A moiety, explains their tight binding to endotoxin. At a structural level, asymmetric distribution of the charged polar residues on one face of the helix and non-polar residues on the opposite face appears to correlate with their activity.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Antineutrophil cytoplasmic antibodies directed against bactericidal/permeability-increasing protein detected in children with cystic fibrosis inhibit neutrophil-mediated killing of Pseudomonas aeruginosa

Antineutrophil cytoplasmic antibodies (ANCA) directed against bactericidal/permeability-increasing protein (BPI) were repeatedly found in cystic fibrosis (CF) patients. We analyzed the effect of BPI-ANCA in inhibiting neutrophil-mediated killing of Pseudomonas aeruginosa. The bactericidal effect expressed as percentage of killed bacteria after 1 h incubation with neutrophils was 55% when the neutrophils were pretreated with normal human serum, ranged from 49 to 63% with the sera from control BPI-ANCA-negative groups and sharply decreased to the mean 30.5% (range 8-51%) in the presence of BPI-ANCA. Furthermore, the effect mediated by BPI-ANCA was dose dependent and reflected the titer of BPI-ANCA in tested sera.

Endotoxin as a drug target

OBJECTIVE

To review the preclinical and clinical evidence that antiendotoxin therapeutic strategies are potentially useful in the prevention and treatment of septic shock.

STUDY DESIGN

A critical review of the literature over the past 30 yrs relating basic and clinical research on the therapeutic value of endotoxin as a target for the prevention and treatment of severe sepsis and septic shock.

MAIN RESULTS

Bacterial endotoxin is a potent and predominant microbial mediator that induces an intense inflammatory and procoagulant response by elements of the innate immune response. This macromolecule is capable of inducing lethal septic shock in experimental animals, and a large number of preclinical studies consistently demonstrate the survival advantage of endotoxin inhibition in experimental models of sepsis. Clinical studies indicate that endotoxin may be found in the systemic circulation in the majority of humans with septic shock. Endotoxemia is largely independent of the nature of the infecting microorganism despite the fact that this molecule is specifically found in the outer membrane of Gram-negative bacteria only. Antiendotoxin strategies studied thus far have not provided reproducible survival benefits in clinical trials in septic patients.

CONCLUSIONS

Despite compelling evidence of the critical importance of endotoxin in the pathogenesis of Gram-negative bacterial sepsis in preclinical investigations and numerous clinical interventional trials, the utility of antiendotoxin approaches to significantly reduce the mortality rate in human septic shock remains unproven. Ongoing clinical trials with specific endotoxin inhibitors should determine the potential value of this therapeutic approach to the management of septic shock.

Antimicrobial peptides in amniotic fluid: defensins, calprotectin and bacterial/permeability-increasing protein in patients with microbial invasion of the amniotic cavity, intra-amniotic inflammation, preterm labor and premature rupture of membranes

OBJECTIVE

Neutrophil defensins (HNP 1-3), bactericidal/permeability-increasing protein (BPI) and calprotectin (MRP8/14) are antimicrobial peptides stored in leukocytes that act as effector molecules of the innate immune response. The purpose of this study was to determine whether parturition, premature rupture of the membranes (PROM) and microbial invasion of the amniotic cavity (MIAC) are associated with changes in amniotic fluid concentrations of these antimicrobial peptides.

STUDY DESIGN

Amniotic fluid was retrieved by amniocentesis from 333 patients in the following groups: group 1, mid-trimester with a subsequent normal pregnancy outcome (n = 84); group 2, preterm labor and intact membranes without MIAC who delivered at term (n = 36), or prematurely (n = 52) and preterm labor with MIAC (n = 26); group 3, preterm PROM with (n = 26) and without (n = 26) MIAC; and group 4, term with intact membranes in the absence of MIAC, in labor (n = 52) and not in labor (n = 31). The concentrations of HNP 1-3, BPI and calprotectin in amniotic fluid were determined by specific and sensitive immunoassays. Placentae of patients in both preterm labor with intact membranes and preterm PROM groups who delivered within 72 h of amniocentesis were examined. Non-parametric statistics, receiver-operating characteristic (ROC) curves and Cox regression models were used for analysis. A p value of < 0.05 was considered statistically significant.

RESULTS

Intra-amniotic infection was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin in both women with preterm labor and intact membranes, and women with preterm PROM. Preterm PROM was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin. Preterm parturition was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin, while parturition at term was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3. Among patients with preterm labor and intact membranes, elevation of amniotic fluid HNP 1-3, BPI and calprotectin concentrations was associated with intra-amniotic inflammation, histological chorioamnionitis and a shorter interval to delivery.

CONCLUSION

MIAC, preterm parturition and preterm PROM are associated with increased amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin. Moreover, elevated amniotic fluid concentrations of BPI, immunoreactive HNP 1-3 and calprotectin are associated with intra-amniotic inflammation, histological chorioamnionitis and shorter amniocentesis-to-delivery interval in patients presenting with preterm labor with intact membranes.

Cloning and characterization of the homolog of mammalian lipopolysaccharide-binding protein and bactericidal permeability-increasing protein in rainbow trout Oncorhynchus mykiss

We cloned two cDNAs denoted as RT-LBP/BPI-1 and RT-LBP/BPI-2, respectively, which were derived from the mRNA of head kidney from rainbow trout. They showed structural homology with LPS-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI) in mammals. The full-length cDNA of RT-LBP/BPI-1 and RT-LBP/BPI-2 is 1666 and 1741 bp, respectively. Both cDNAs encoded 473 aa residues, including the amino acids conserved in mammalian LBP and BPI proteins that were assumed to be involved in LPS binding. The overall coding sequence of RT-LBP/BPI-1 has 33% amino acid homology to human LBP and 34% to human BPI, and RT-LBP/BPI-2 has 32% amino acid homology to human LBP and 33% to human BPI. Three-dimensional structure analysis by three-dimensional/one-dimensional (3D-1D) methods also demonstrated that RT-LBP/BPI-1 and RT-LBP/BPI-2 proteins showed significant similarity to human BPI, having a boomerang shape with N-terminal and C-terminal barrels. Phylogenetic analysis showed that the LBP and BPI genes seemed to be established after the divergence of mammals from teleosts. These results suggested that RT-LBP/BPI-1 and RT-LBP/BPI-2 may be a putative ortholog for mammalian LBP and/or BPI genes. This is the first study to identify the LBP family genes from nonmammalian vertebrates.

Plunc, a member of the secretory gland protein family, is up-regulated in nasal respiratory epithelium after olfactory bulbectomy

Subtraction suppression hybridization was used with high throughput screening to identify transcripts of genes that are differentially expressed in nasal epithelium following lesioning of the olfactory bulb, termed bulbectomy. We isolated the rat homologue of plunc, a murine gene highly expressed in lung and nasopharyngeal regions, by this method. Rat plunc encodes a 270-amino acid protein containing a putative signal peptide. plunc up-regulation in respiratory epithelium was confirmed by Northern blot and in situ hybridization. plunc mRNA was expressed in nasal epithelium, heart, lung, thymus, and salivary gland in adult rodent. plunc was expressed in nasal epithelium, thymus, and salivary gland during embryogenesis. Antibodies against Plunc detected a 31-kDa protein in lung, heart, and spleen. Rat nasal epithelium displayed robust immunoreactivity that was highly localized to the microvilli layer of respiratory epithelium. The expression of plunc was up-regulated after bulbectomy in respiratory epithelium. We also detected secreted plunc in rat and human mucus. Sequence and homology analyses suggest that Plunc is a member of the secretory gland protein family with putative bactericidal/bacteriostatic function. This is the first protein found in respiratory epithelium whose expression is regulated by olfactory neuronal injury and may provide protection against infection subsequent to injury.

Bacterial lipopolysaccharides and innate immunity

Bacterial lipopolysaccharides (LPS) are the major outer surface membrane components present in almost all Gram-negative bacteria and act as extremely strong stimulators of innate or natural immunity in diverse eukaryotic species ranging from insects to humans. LPS consist of a poly- or oligosaccharide region that is anchored in the outer bacterial membrane by a specific carbohydrate lipid moiety termed lipid A. The lipid A component is the primary immunostimulatory centre of LPS. With respect to immunoactivation in mammalian systems, the classical group of strongly agonistic (highly endotoxic) forms of LPS has been shown to be comprised of a rather similar set of lipid A types. In addition, several natural or derivatised lipid A structures have been identified that display comparatively low or even no immunostimulation for a given mammalian species. Some members of the latter more heterogeneous group are capable of antagonizing the effects of strongly stimulatory LPS/lipid A forms. Agonistic forms of LPS or lipid A trigger numerous physiological immunostimulatory effects in mammalian organisms, but--in higher doses--can also lead to pathological reactions such as the induction of septic shock. Cells of the myeloid lineage have been shown to be the primary cellular sensors for LPS in the mammalian immune system. During the past decade, enormous progress has been obtained in the elucidation of the central LPS/lipid A recognition and signaling system in mammalian phagocytes. According to the current model, the specific cellular recognition of agonistic LPS/lipid A is initialized by the combined extracellular actions of LPS binding protein (LBP), the membrane-bound or soluble forms of CD14 and the newly identified Toll-like receptor 4 (TLR4)*MD-2 complex, leading to the rapid activation of an intracellular signaling network that is highly homologous to the signaling systems of IL-1 and IL-18. The elucidation of structure-activity correlations in LPS and lipid A has not only contributed to a molecular understanding of both immunostimulatory and toxic septic processes, but has also re-animated the development of new pharmacological and immunostimulatory strategies for the prevention and therapy of infectious and malignant diseases.

Neutrophil specific granule deficiency and mutations in the gene encoding transcription factor C/EBP(epsilon)

Neutrophil specific granule deficiency (SGD) is a rare congenital disorder. The neutrophils of these patients display atypical bilobed nuclei; lack expression of at least one primary and all secondary and tertiary granule proteins; and possess defects in chemotaxis, disaggregation, receptor upregulation, and bactericidal activity. SGD patients suffer frequent and severe bacterial infections. Although the first of five patients worldwide was reported in the early 1970s, the molecular basis for the defect was discovered only recently. This review presents data implicating the functional loss of the myeloid transcription factor CCAAT/enhancer binding protein (C/EBP(epsilon)) as a causative agent in the development of SGD. The murine model for SGD provides evidence for defects in eosinophil granule gene expression and indicates abnormalities in macrophage maturation and function. Deficiencies in multiple myeloid lineages, in addition to neutrophils, indicate the importance of C/EBP(epsilon) in regulating important innate immune and inflammatory responses critical for host defense.

Bactericidal/permeability-increasing protein promotes complement activation for neutrophil-mediated phagocytosis on bacterial surface

The neutrophil bactericidal/permeability-increasing protein (BPI) has both bactericidal and lipopolysaccharide-neutralizing activities. The present study suggests that BPI also plays an important role in phagocytosis of Escherichia coli by neutrophils through promotion of complement activation on the bacterial surface. Flow cytometric analysis indicated that fluorescein-labelled E. coli treated with BPI were phagocytosed in the presence of serum at two- to five-fold higher levels than phagocytosis of the bacteria without the treatment. In contrast, phagocytosis of the fluoresceined bacteria with or without treatment by BPI did not occur at all in the absence of serum. The phagocytosis stimulated by BPI and serum was dose-dependent. The effect of BPI on phagocytosis in the presence of serum was not observed on Gram-positive bacteria (Staphylococcus aureus). Interestingly, the complement C3b/iC3b fragments were deposited onto the bacterial surface also as a function of the BPI concentration under conditions similar to those for phagocytosis. Furthermore, the BPI-promoted phagocytosis was blocked completely by anti-C3 F(ab')(2) and partially by anti-complement receptor (CR) type 1 and/or anti-CR type 3. These findings suggest that BPI accelerates complement activation to opsonize bacteria with complement-derived fragments, leading to stimulation of phagocytosis by neutrophils via CR(s).

Isolation and characterization of four bactericidal domains in the bovine beta-lactoglobulin

Proteolytic digestion of bovine beta-lactoglobulin by trypsin yielded four peptide fragments with bactericidal activity. The peptides were isolated and their sequences were found as follows: VAGTWY (residues 15-20), AASDISLLDAQSAPLR (residues 25-40), IPAVFK (residues 78-83) and VLVLDTDYK (residues 92-100). The four peptides were synthesized and found to exert bactericidal effects against the Gram-positive bacteria only. In order to understand the structural requirements for antibacterial activity, the amino acid sequence of the peptide VLVLDTDYK was modified. The replacement of the Asp (98) residue by Arg and the addition of a Lys residue at the C-terminus yielded the peptide VLVLDTRYKK which enlarged the bactericidal activity spectrum to the Gram-negative bacteria Escherichia coli and Bordetella bronchiseptica and significantly reduced the antibacterial capacity of the peptide toward Bacillus subtilis. By data base searches with the sequence VLVLDTRYKK a high homology was found with the peptide VLVATLRYKK (residues 55-64) of human blue-sensitive opsin, the protein of the blue pigment responsible for color vision. A peptide with this sequence was synthesized and assayed for bactericidal activity. VLVATLRYKK was strongly active against all the bacterial strains tested. Our results suggest a possible antimicrobial function of beta-lactoglobulin after its partial digestion by endopeptidases of the pancreas and show moreover that small targeted modifications in the sequence of beta-lactoglobulin could be useful to increase its antimicrobial function.

Neutrophil-specific granule deficiency: homozygous recessive inheritance of a frameshift mutation in the gene encoding transcription factor CCAAT/enhancer binding protein--epsilon

Neutrophil-specific granule deficiency (SGD) is a rare congenital disorder. The neutrophils of individuals with SGD display atypical bi-lobed nuclei, lack expression of all secondary and tertiary granule proteins, and possess defects in chemotaxis, disaggregation, receptor up-regulation, and bactericidal activity, resulting in frequent and severe bacterial infections. Previously, a homozygous mutation in the CCAAT/enhancer binding protein-epsilon (C/EBPepsilon) gene was reported for one case of SGD. To substantiate the role of C/EBPepsilon in the development of SGD and elucidate its mechanism of inheritance, the mutational status of the gene was determined in a second individual. An A-nucleotide insertion in the coding region of the C/EBPepsilon gene was detected. This mutation completely abolished the predicted translation of all C/EBPepsilon isoforms. Microsatellite and nucleotide sequence analyses of the C/EBPepsilon locus in the parents of the proband indicated that the disorder may have resulted from homozygous recessive inheritance of the mutant allele from an ancestor shared by both parents. The mutant C/EBPepsilon(32) protein localized in the cytoplasm rather than the nucleus and was unable to activate transcription. Consistent with this, a significant decrease in the levels of the messenger RNAs (mRNAs) encoding the secondary granule protein human 18-kd cationic antimicrobial protein (hCAP-18)/LL-37 and the primary granule protein bactericidal/permeability-increasing protein were observed in the patient. The hCAP-18 mRNA was induced by overexpression of C/EBPepsilon(32) in the human myeloid leukemia cell line, U937, supporting the hypothesis that C/EBPepsilon is a key regulator of granule gene synthesis. This study strongly implicates mutation of the C/EBPepsilon gene as the primary genetic defect involved in the development of neutrophil SGD and defines its mechanism of inheritance.

Efficacy of bactericidal/permeability-increasing protein in experimental otitis media with effusion in rats: a new therapy for mucosal infections

Otitis media with effusion (OME) is characterized by the presence of fluid in the middle ear without signs or symptoms of acute infection and by persistent changes in the middle ear mucosa. These are mainly induced by gram-negative bacterial infection and dysfunction of the eustachian tube (ET). Gram-negative bacteria (GNB) contain lipopolysaccharide (LPS) in their outer membrane that is responsible for inflammatory reactions in the middle ear. In this study we investigated the therapeutic effect of a recombinant LPS-binding protein, bactericidal/permeability-increasing protein (rBPI21), on the repair of mucosal damage in rats with experimentally induced OME. OME was induced by obstruction of the eustachian tube in combination with LPS injection. Twelve weeks after OME induction, secretory cells in the tympanic orifice of the middle ear were increased from an average of 14 +/- 2 to 31 +/- 5, ciliated cells were decreased from 24 +/- 4 to 6 +/- 4, and the number of macrophages in the subepithelial layer increased from 13 +/- 4 to 27 +/- 3. A single dose of rBPI21 was administered directly into the middle ear cavity 2 weeks after the induction of OME. Histologic examination of the middle ear mucosa at 4 and 12 weeks after OME induction showed that mucosal changes were restored by rBPI21 treatment. These results demonstrate that the middle ear mucosa recovers from inflammatory changes associated with OME after treatment with rBPI21. This suggests that rBPI21 may be useful in the treatment of OME and of mucosal infections of the respiratory tract.

Construction of acetate auxotrophs of Neisseria meningitidis to study host-meningococcal endotoxin interactions

To facilitate studies of the molecular determinants of host-meningococcal lipooligosaccharide (endotoxin) interactions at patho-physiologically relevant endotoxin concentrations (i.e. < or =10 ng/ml), we have generated acetate auxotrophs NMBACE1 from encapsulated Neisseria meningitidis (serogroup B, strain NMB) and NMBACE2 from an isogenic bacterial mutant lacking the polysialic acid capsule. Growth of the auxotrophs in medium containing [(14)C]acetate yielded (14)C-lipooligosaccharides containing approximately 600 cpm/ng. Gel sieving resolved 14C-lipooligosaccharide-containing aggregates with an estimated molecular mass of > or =20 x 10(6) Da (peak A) and approximately 1 x 10(6) Da (peak B) from both strains. Lipooligosaccharides in peaks A and B had the same fatty acid composition and SDS-polyacrylamide gel electrophoresis profile. 14C-Labeled capsule copurified with (14)C-lipooligosaccharides in peak B from NMBACE1, whereas the other aggregates contained only 14C-lipooligosaccharide. For all aggregates, lipopolysaccharide-binding protein and soluble CD14-induced delivery of lipooligosaccharides to endothelial cells and cell activation correlated with disaggregation of lipooligosaccharides. These processes were inhibited by the presence of capsule but unaffected by the size of the aggregates. In contrast, endotoxin activation of cells containing membrane CD14 was unaffected by capsule but diminished when endotoxin was presented in larger aggregates. These findings demonstrate that the physical presentation of lipooligosaccharide, including possible interactions with capsule, affect the ability of meningococcal endotoxin to interact with and activate specific host targets.

Isolation, partial characterization, and concentration in experimental sepsis of baboon lipopolysaccharide-binding protein

Lipopolysaccharide-binding protein (LBP) is important for mediating host responses to lipopolysaccharide (LPS). The structure and properties of human, rabbit, and murine LBP have been previously described. In this study we partially characterized baboon LBP and investigated its appearance in experimental sepsis. Recurrent bacteremia was induced in baboons by infusion of live Escherichia coli organisms over a 2-hour period at 0, 24, and 48 hours. To assay baboon plasma LBP levels, an enzyme-linked immunosorbent assay with cross-reactive antibodies to human LBP was developed. Control baboon plasma LBP concentrations were 2 to 5 microg/mL. During experimental sepsis, baboon plasma LBP levels increased to between 200 and 350 microg/mL and in parallel with the increase in C-reactive protein levels. Baboon LBP was isolated from acute phase serum by ion-exchange chromatography followed by immuno-affinity chromatography. Its NH2-terminal sequence (XNPGLVARTTNKGLEYSAQE) and its molecular weight (approximately 60 kd) were determined and were proved to be highly homologous to human LBP.

What are the microbial components implicated in the pathogenesis of sepsis? Report on a symposium

Despite considerable efforts in the past quarter century to improve therapy for sepsis, mortality rates remain unacceptably high. Microbe-derived constituents can induce the host to produce many mediators that can contribute to immune dysregulation, tissue damage, and death. Although endotoxin-mediated events are clearly important in gram-negative infections, gram-positive bacteria can also play a dominant role. Understanding the interplay of microbial constituents and host immune or inflammatory responses prompted a meeting at Rockefeller University in May 1998. Participants discussed the relative merits of a "2-hit" hypothesis to explain the course of lethal septic shock and a "multihit" synergistic threshold hypothesis. Recommendations include the following: (1) developing animal models that closely mimic human sepsis; (2) further investigating antibiotic effects on bacteria; (3) assessing the relationships between endotoxin, prokaryotic DNA, and peptidoglycan (i.e., independent, additive, or synergistic) in inducing host responses; and (4) developing new strategies to improve outcomes. Studies are needed to better define which and how different microbial constituents lead to sepsis and to provide critical leads for therapeutic intervention.

Identification of constituents of human neutrophil azurophil granules that mediate fungistasis against Histoplasma capsulatum

Previously we demonstrated that human neutrophils mediate potent and long-lasting fungistasis against Histoplasma capsulatum yeasts and that all of the fungistatic activity resides in the azurophil granules. In the present study, specific azurophil granule constituents with fungistatic activity were identified by incubation with H. capsulatum yeasts for 24 h and by quantifying the subsequent growth of yeasts via the incorporation of [(3)H]leucine. Human neutrophil defensins HNP-1, HNP-2, and HNP-3 inhibited the growth of H. capsulatum yeasts in a concentration-dependent manner with maximum inhibition at 8 microg/ml. At a concentration of 4 microg/ml, all possible paired combinations of defensins exhibited additive fungistatic activity against H. capsulatum yeasts. Cathepsin G and bactericidal-permeability-increasing protein (BPI) also mediated fungistasis against H. capsulatum in a concentration-dependent manner. The fungistatic activities of combinations of cathepsin G and BPI were additive, as were those of combinations of cathepsin G or BPI with HNP-1, HNP-2, and HNP-3. Lysozyme and elastase exhibited modest antifungal activity, and azurocidin and proteinase 3 exhibited no significant fungistasis against H. capsulatum yeasts. Thus, defensins, cathepsin G, and BPI are the major anti-H. capsulatum effector molecules in the azurophil granules of human neutrophils.

Basic residues of human group IIA phospholipase A2 are important for binding to factor Xa and prothrombinase inhibition comparison with other mammalian secreted phospholipases A2

Human secreted group IIA phospholipase A2 (hGIIA) was reported to inhibit prothrombinase activity because of binding to factor Xa. This study further shows that hGIIA and its catalytically inactive H48Q mutant prolong the lag time of thrombin generation in human platelet-rich plasma with similar efficiency, indicating that hGIIA exerts an anticoagulant effect independently of phospholipid hydrolysis under ex vivo conditions. Charge reversal of basic residues on the interfacial binding surface (IBS) of hGIIA leads to decreased ability to inhibit prothrombinase activity, which correlates with a reduced affinity for factor Xa, as determined by surface plasmon resonance. Mutation of other surface-exposed basic residues, hydrophobic residues on the IBS, and His48, does not affect the ability of hGIIA to inhibit prothrombinase activity and bind to factor Xa. Other basic, but not neutral or acidic, mammalian secreted phospholipases A2 (sPLA2s) exert a phospholipid-independent inhibitory effect on prothrombinase activity, suggesting that these basic sPLA2s also bind to factor Xa. In conclusion, this study demonstrates that the anticoagulant effect of hGIIA is independent of phospholipid hydrolysis and is based on its interaction with factor Xa, leading to prothrombinase inhibition, even under ex vivo conditions. This study also shows that such an interaction involves basic residues located on the IBS of hGIIA, and suggests that other basic mammalian sPLA2s may also inhibit blood coagulation by a similar mechanism to that described for hGIIA.

Bactericidal/permeability-increasing protein (BPI) inhibits angiogenesis via induction of apoptosis in vascular endothelial cells

Bactericidal/permeability-increasing protein (BPI) has been known for some time to function in killing bacteria and in neutralizing the effects of bacterial endotoxin lipopolysaccharide. In the present study, BPI is found to be a novel endogenous inhibitor of angiogenesis. Within the sub-μM range, BPI shows a concentration-dependent inhibition of endothelial cell (EC) proliferation that is mediated by cell detachment and subsequent induction of apoptosis. As measured by flow cytometric analysis of the percentage of subdiploid cells, apoptosis induction was half-maximal at about 250 nmol/L BPI. Apoptosis was confirmed by quantification of cells with nuclear fragmentation. Apoptosis was found to be EC specific. In an in vitro collagen gel-based angiogenesis assay, BPI at 1.8 μmol/L inhibited tube formation by 81% after only 24 hours. Evidence for in vivo inhibition of angiogenesis was obtained, using the chorioallantoic membrane assay in which BPI was seen to be significantly effective at concentrations as low as 180 nmol/L. This newly discovered function of BPI might provide a possible therapeutic modality for the treatment of various pathologic disorders that depend on angiogenesis.

Effect of lysozyme or modified lysozyme fragments on DNA and RNA synthesis and membrane permeability of Escherichia coli

Previously we have shown that chicken egg white lysozyme, an efficient bactericidal agent, affects both gram-positive and gram-negative bacteria independently of its muramidase activity. More recently we reported that the digestion of lysozyme by clostripain yielded a pentadecapeptide, IVSDGNGMNAWVAWR (amino acid 98-112 of chicken egg white lysozyme), with moderate bactericidal activity but without muramidase activity. On the basis of this amino acid sequence three polypeptides, in which asparagine 106 was replaced by arginine (IVSDGNGMRAWVAWR, RAWVAWR, RWVAWR), were synthesized which showed to be strongly bactericidal. To elucidate the mechanisms of action of lysozyme and of the modified antimicrobial polypeptides Escherichia coli strain ML-35p was used. It is an ideal organism to study the outer and the inner membrane permeabilization since it is cryptic for periplasmic beta-lactamase and cytoplasmic beta-galactosidase unless the outer or inner membrane becomes damaged. For the first time we present evidence that lysozyme inhibits DNA and RNA synthesis and in contrast to the present view is able to damage the outer membrane of Escherichia coli. Blockage of macromolecular synthesis, outer membrane damage and inner membrane permeabilization bring about bacterial death. Ultrastructural studies indicate that lysozyme does not affect bacterial morphology but impairs stability of the organism. The bactericidal polypeptides derived from lysozyme block at first the synthesis of DNA and RNA which is followed by an increase of the outer membrane permeabilization causing the bacterial death. Inner membrane permeabilization, caused by RAWVAWR and RWVAWR, follows after the blockage of macromolecular synthesis and outer membrane damage, indicating that inner membrane permeabilization is not the deadly event. Escherichia coli bacteria killed by the substituted bactericidal polypeptides appeared, by electron microscopy, with a condensed cytoplasm and undulated bacterial membrane. So the action of lysozyme and its derived peptides is not identical.

Bactericidal/permeability-increasing protein (BPI) inhibits angiogenesis via induction of apoptosis in vascular endothelial cells

Bactericidal/permeability-increasing protein (BPI) has been known for some time to function in killing bacteria and in neutralizing the effects of bacterial endotoxin lipopolysaccharide. In the present study, BPI is found to be a novel endogenous inhibitor of angiogenesis. Within the sub-μM range, BPI shows a concentration-dependent inhibition of endothelial cell (EC) proliferation that is mediated by cell detachment and subsequent induction of apoptosis. As measured by flow cytometric analysis of the percentage of subdiploid cells, apoptosis induction was half-maximal at about 250 nmol/L BPI. Apoptosis was confirmed by quantification of cells with nuclear fragmentation. Apoptosis was found to be EC specific. In an in vitro collagen gel-based angiogenesis assay, BPI at 1.8 μmol/L inhibited tube formation by 81% after only 24 hours. Evidence for in vivo inhibition of angiogenesis was obtained, using the chorioallantoic membrane assay in which BPI was seen to be significantly effective at concentrations as low as 180 nmol/L. This newly discovered function of BPI might provide a possible therapeutic modality for the treatment of various pathologic disorders that depend on angiogenesis.

Formate protects stationary-phase Escherichia coli and Salmonella cells from killing by a cationic antimicrobial peptide

For a sustained infection, enteric bacterial pathogens must evade, resist or tolerate a variety of antimicrobial host defence peptides and proteins. We report here that specific organic acids protect stationary-phase Escherichia coli and Salmonella cells from killing by a potent antimicrobial peptide derived from the human bactericidal/permeability-increasing protein (BPI). BPI-derived peptide P2 rapidly halted oxygen consumption by stationary-phase cells preincubated with glucose, pyruvate or malate and caused a 109-fold drop in cell viability within 90 min of addition. In marked contrast, O2 consumption and viability were not significantly affected in stationary-phase cells preincubated with formate or succinate. Experiments with fdhH, fdoG, fdnG, selC and sdhO mutants indicate that protection by formate and succinate requires their oxidation by the Fdh-N formate dehydrogenase and succinate dehydrogenase respectively. Protection was also dependent on the BipA GTPase but did not require the RpoS sigma factor. We conclude that the primary lesion caused by this cationic peptide is not gross permeabilization of the bacterial cytoplasmic membrane but may involve specific disruption of the respiratory chain. Because P2 shares sequence similarity with a range of other antimicrobial peptides, its cytotoxic mechanism has broader significance. Additionally, protective quantities of formate are secreted by E. coli and Salmonella during growth suggesting that such compounds are important determinants of bacterial survival in the host.

Inclusion of S-sepharose beads in the culture medium significantly improves recovery of secreted rBPI(21) from transfected CHO-K1 cells

rBPI(23), a recombinant N-terminal fragment of human bactericidal/permeability-increasing protein (BPI), kills gram-negative bacteria and binds endotoxin. rBPI(21), a variant, in which cysteine 132 is changed to alanine, retains the activities of rBPI(23). Initial attempts using conventional ion-exchange chromatography to purify rBPI(23) from culture supernatants of transfected CHO-K1 cells resulted in lower than expected yields. Also, ELISA of supernatants from CHO-K1 transfectants expressing rBPI(23) or rBPI(21) yielded variable signals. Results from pulse-chase experiments using [(35)S]methionine had indicated that rBPI(23) could not be detected in the culture medium by 7 h of chase, suggesting that these proteins were degraded and/or bound to cells, media components, or vessel surfaces. To address these issues, we developed a novel process whereby sterile S-Sepharose beads were added directly to the cell culture medium. For attached cells, the beads were added to confluent cultures with serum-free medium for the expression phase, while for suspension-adapted cells, beads were added at the beginning of culture growth. The S-Sepharose was then separated from cells and media and washed, and BPI was eluted with high-salt buffer. This approach yielded up to a 50-fold improvement in recovery of rBPI(23) and rBPI(21) from roller bottles, shake flasks, and 2-liter fermenters. It also resulted in improved detection and quantitation of secreted rBPI(23) and rBPI(21) by ELISA. Results of competition binding studies with iodinated rBPI(21) in conjunction with unlabeled rBPI(21) and rBPI(23) or with heparin demonstrated that these proteins bound specifically and with high affinity to heparan-containing sites on the surface of the CHO-K1 cells. We conclude that the S-Sepharose included in the culture medium captures the BPI protein products as they are secreted and protects them from degradation and/or irreversible binding to cell surfaces. This method has been scaled up to a manufacturing process in large (2750 liter) fermenters for pharmaceutical production.

Surface plasmon resonance studies resolve the enigmatic endotoxin neutralizing activity of polymyxin B

Polymyxin B (PMB), a cyclic cationic peptide antibiotic, despite its severe side effects continues to occupy a premiere position for treating endotoxicosis. Its mode of neutralization of endotoxin has remained elusive for the last three decades. Several synthetic peptide mimics of PMB, capable of binding endotoxin, have been made. However, the binding ability alone appears to be a deceptive indicator of endotoxin neutralizing activity as molecules with similar binding propensities could either sequester or opsonize the toxin. Hence identification of additional physical parameters which describe adequately the outcome of PMB-endotoxin interaction become imperative. Surface plasmon resonance (SPR) studies reported here show that several mimics of PMB despite exhibiting lipopolysaccharide binding affinities comparable with it but, unlike it, do not sequester the endotoxin. These studies thus provide a striking illustration of the difference in the behavior of PMB, vis a vis its mimics toward the endotoxin lamellae, and define further, in chemical terms, mechanism of the action of PMB and allow us to posit that the design of molecules as effective antidotes for sepsis should incorporate the ability to sequester endotoxin specifically.