The role of bactericidal/permeability-increasing protein in the treatment of primate bacteremia and septic shock

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.

Effects of bactericidal/permeability-increasing protein on endotoxin-induced fever and Escherichia coli-induced shock in rabbits

Binding of bactericidal/permeability-increasing protein (BPI) to endotoxin inhibits endotoxin-triggered responses. We investigated the effects of BPI on endotoxin fever and E. coli-induced septic shock in rabbits. Pre-incubation of endotoxin with BPI blocked fever compared to control rabbits (n = 6). A marked reduction in fever was also observed when BPI was injected before endotoxin. E. coli-challenge resulted in 66% mortality (n = 6); pre-treatment with BPI resulted in survival of all animals (n = 3). Mean arterial blood pressure was higher in BPI-treated compared to control rabbits. Comparable leukopenia and thrombocytopenia was observed with either BPI or vehicle treatment. Tumor necrosis factor (TNF) and interleukin-1 receptor antagonist were similarly elevated in both BPI- and saline-treated rabbits. However, in BPI treated rabbits, peak TNF levels were 34 % lower compared to saline controls ( P < 0.05). Further studies are warranted to assess whether BPI may have therapeutic potential for the treatment of septic shock.

An N-terminal fragment of bactericidal/permeability-increasing protein protects against hemodynamic and metabolic derangements in rat Gram-negative sepsis

Recombinant N-terminal fragments of bactericidal/permeability-increasing protein (BPI) are protective in acute models of endotoxemia or bacteremia. However, their usefulness in models utilizing slow infusion of bacteria has not been reported. Anesthetized rats were infused with Escherichia coli 07:K1 bacteria (5 x 109 cfu/h) for 2 h. Hemodynamics, glucose and lactate levels, tumor necrosis factor-α (TNFα) and endotoxin levels were measured for 210 min. The rats were treated with a 2 h infusion of RBPI21 or thaumatin (10 mg/kg/h), a protein that does not bind endotoxin but is similar to rBPI21 in molecular weight and isoelectric point. Control rats received only saline and vehicle. In animals treated with thaumatin, blood pressure, cardiac index and stroke volume declined rapidly (within 30 min). After 90 min glucose levels were significantly depressed whereas lactate was elevated. Endotoxemia (764 ± 353 ng/ml) was observed within 30 min. rBPI 21 significantly reduced the cardiovascular depression observed after 30 min and abolished all hemodynamic responses by the end of the experiment. rBPI21 significantly reduced hypoglycemia, elevated lactate levels, and endotoxin levels after 90 min. These results indicate that reduction of endotoxin levels resulting from RBPI21 therapy leads to significant protection in this model of acute Gram-negative bacterial sepsis.

Anti-endotoxin properties of cationic host defence peptides and proteins

The innate immune system of mammals contains a series of peptides with overall positive charge and an amphipathic structure which have a variety of important properties in host defences. Although these are often termed cationic antimicrobial peptides, they have numerous roles in innate defences in all complex species of life and thus we prefer to refer to them as host defence peptides. These roles include: (i) an ability to kill micro-organisms directly, ranging from bacteria to viruses, fungi, parasites and helminths; (ii) an adjuvant activity in the adaptive response; and (iii) a multiplicity of roles in modulating innate immunity, including an apparent ability to stimulate protective innate immunity while suppressing harmful inflammatory/septic responses. This latter property may be one of the more important activities of these peptides in vivo. Innate immunity is thought to be triggered by the interaction of conserved bacterial components with particular receptors including Toll-like receptors (TLRs) on host cells. However, the initiation of the innate immune response through this route may trigger a pro-inflammatory cascade that is the principle cause of harmful conditions such as sepsis. Since we are exposed to potentially dangerous pathogens on a daily basis, the host response must contain certain checks and balances. We propose that host defence peptides have a role in feed-back modulation of inflammation under normal (low-pathogen exposure) conditions. This review surveys the available information regarding the antiendotoxic/anti-inflammatory properties of host defence peptides, and will address whether this potential might be exploited for therapeutic benefit in sepsis.

A peptide derived from human bactericidal/permeability-increasing protein (BPI) exerts bactericidal activity against Gram-negative bacterial isolates obtained from clinical cases of bovine mastitis

Gram-negative bacteria are responsible for approximately one-third of the clinical cases of bovine mastitis and can elicit a life-threatening, systemic inflammatory response. Lipopolysaccharide (LPS) is a membrane component of Gram-negative bacteria and is largely responsible for evoking the inflammatory response. Antibiotic and anti-inflammatory therapy for treating Gram-negative infections remains suboptimal. Bactericidal/permeability-increasing protein (BPI) is a neutrophil-derived protein with antimicrobial and LPS-neutralizing properties. Select peptide derivatives of BPI are reported to retain these properties. The objective of this study was to evaluate the antimicrobial activity of a human BPI-derived synthetic peptide against clinical bovine mastitis isolates of Gram-negative bacteria. A hybrid peptide was synthesized corresponding to two regions of human BPI (amino acids 90-99 and 148-161), the former of which has bactericidal activity and the latter of which has LPS-neutralizing activity. The minimum inhibitory (MIC) and bactericidal (MBC) concentrations of this peptide against various genera of bacteria were determined using a broth microdilution assay. The MIC's were determined to be: 16-64 microg/ml against Escherichia coli; 32-128 microg/ml against Klebsiella pneumoniae and Enterobacter spp.; and 64-256 microg/ml against Pseudomonas aeruginosa. The MBC's were equivalent to or 1-fold greater than corresponding MIC's. The peptide had no growth inhibitory effect on Serratia marcescens. The antimicrobial activity of the peptide was retained in the presence of serum, but severely impaired in milk. Further functional evaluation of the peptide demonstrated its ability to completely neutralize LPS. Together, these data support additional investigations into the therapeutic application of BPI to the treatment of Gram-negative infections in cattle.

The therapeutic potential of cationic peptides

Novel classes of antibiotics that are useful against resistant bacteria are a major need in human medicine. Cationic antimicrobial peptides are utilised as nature's antibiotics, being produced constitutively or in response to infection in virtually every type of organism from plants and insects to man. Thus, these peptides are now being considered as potential antibiotics for infections. They have the following assets: structural diversity, rapid bactericidal action, a broad spectrum of activity that includes most of the clinically important resistant pathogens, and several ancillary activities which can include antifungal, antiviral, anti-endotoxin activities, and promotion of wound healing. Cationic peptides and proteins are now proceeding through clinical trials as topical antibiotics and anti-endotoxins.

Influence of the TNF-alpha and TNF-beta polymorphisms upon infectious risk and outcome in surgical intensive care patients

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) is a well-documented central inflammatory mediator in sepsis. Specific polymorphisms of the TNF-alpha and TNF-beta genes (TNF2 and LTA + 250, respectively) have been suggested to correlate with higher mortality in septic shock. This study sought to determine whether these polymorphisms of the TNF-alpha and -beta genes are associated with an increased risk of infection in an at-risk surgical intensive care population.

MATERIALS AND METHODS

Forty-four consecutive patients with systemic inflammatory response syndrome were enrolled prospectively in the study. Genomic DNA was isolated from whole blood samples using standard phenol/chloroform extraction techniques. Specific fragments including the polymorphic sites of each gene were amplified by polymerase chain reaction, and restriction enzyme digestions were performed. Genotypes were determined by gel electrophoresis and confirmed by direct sequencing.

RESULTS

Eighty-six percent of the patients were TNF1 homozygotes (G:G at -308 of the TNF-alpha promoter region), whereas 9% of the patients were homozygous for TNF2 (A:A). There was no difference in the incidence of sepsis, septic shock, or mortality between patients bearing the various alleles. Only 13.6% of the patients exhibited the G:G alleles for TNF-beta, whereas the homozygous A:A was present in 45.4% of the patients.

CONCLUSION

The presence of the A allele at these polymorphic sites did not predispose critically ill surgical patients to either infection or 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.

Bactericidal/permeability-increasing protein--lessons learned from the phase III, randomized, clinical trial of rBPI21 for adjunctive treatment of children with severe meningococcemia

OBJECTIVES

To review the scientific rationale for the clinical use of recombinant bactericidal permeability-increasing protein (rBPI21) and to discuss the results, implications, and lessons learned during the clinical development of rBPI21 for adjunctive treatment of children with severe meningococcemia.

DATA SOURCES

The published medical literature.

STUDY SELECTION

Of the phase I/II and phase III trials in humans, preclinical experimental studies were selected. Data from these sources are presented in the context of the authors' experiences as principal investigators in the phase I/II and/or phase III clinical trials.

DATA EXTRACTION AND DATA SYNTHESIS

Bactericidal permeability-increasing protein and N-terminal fragments of bactericidal permeability-increasing protein, such as rBPI21, bind and neutralize endotoxin and are potently bactericidal against both smooth and rough forms of Gram-negative bacteria, including Neisseria meningitidis. Based on these properties and compelling preclinical data indicating that administration of rBPI21 reduced mortality in several models of sepsis, we initiated clinical trials by using rBPI21 as adjunctive therapy for children with severe meningococcemia. Data from the phase III, randomized, placebo-controlled trial indicate that rBPI21 reduces clinically significant morbidities and improves the functional outcome of children with severe meningococcemia. No statistically significant benefit in mortality was demonstrated; however, because of the rare incidence of disease and the rapidity of death in this study, the trial was substantially underpowered to detect a statistically significant mortality advantage. Before the completion of the trial, the probability that the study might have been underpowered to detect a significant reduction in mortality was recognized. An attempt at selecting a previously unvalidated composite end point to increase the meaningful event rate for the primary end point proved unsuccessful. Significant improvements were seen in other prospectively defined outcome variables that suggest an overall substantial benefit of therapy with rBPI21 in children with severe meningococcemia.

CONCLUSIONS

As the largest therapeutic trial conducted in pediatric critical care, the phase III trial of rBPI21 demonstrates important principles that can influence the design of future trials targeting rare, life-threatening diseases.

Acute respiratory distress syndrome. Potential pharmacologic interventions

Remarkable progress has been made in the past 10 years with regard to understanding the interplay of potent physiologic mediators in patients with acute lung injury. Because there are so many mediators and the interaction of these agents is complex, true insight into the process has been slow in coming. Clinical studies in ARDS, as well as sepsis, the leading cause of ARDS, have increased in number, size, and quality over this same period. Although none of these studies has produced an accepted new therapy for ARDS, each has laid the groundwork for more efficient and more elegant studies of the problem. The stage is now set for the real advances to be brought forward and put to rigorous, efficient clinical testing.

Antiendotoxin strategies

Endotoxin is a potent stimulator of the inflammatory response and is believed to initiate the pathology in Gram-negative sepsis. Agents are being developed that bind and neutralize or block the effects of endotoxin, with the goal of improving outcome in the treatment of sepsis. Strategies discussed in this article include anti-LPS antibodies, LPS binding proteins and lipoproteins, polymyxin B conjugates, lipid A analogues, and extracorporeal techniques for endotoxin removal.

Protective effect of bactericidal/permeability-increasing protein (rBPI21) in baboon sepsis is related to its antibacterial, not antiendotoxin, properties

OBJECTIVE AND SUMMARY BACKGROUND DATA

The recombinant fragment of bactericidal/permeability-increasing protein, rBPI21, has potent bactericidal activity against gram-negative bacteria as well as antiendotoxin (lipopolysaccharide [LPS]) action. On the basis of these activities, the authors sought to discover whether rBPI21 would be protective in baboons with live Escherichia coli-induced sepsis and whether the potential protective effects of rBPI21 (together with antibiotics) would be more closely related to its antibacterial or LPS-neutralizing effects.

METHODS

In a prospective, randomized, placebo-controlled subchronic laboratory study, the efficacy of rBPI21 or placebo was studied over 72 hours in chronically instrumented male baboons infused with live E. coli under antibiotic therapy.

RESULTS

Intravenous rBPI21 attenuated sepsis-related organ failure and increased survival significantly. Bacteremia was significantly reduced in the rBPI21 group at 2 hours after the start of the E. coli infusion, whereas circulating LPS was less affected. The in vivo formation of tumor necrosis factor was significantly suppressed by the rBPI21 treatment regimen. Microcirculation and organ function were improved.

CONCLUSIONS

In baboon live E. coli sepsis, the salutary effect of rBPI21 results from a more prevalent antibacterial than antiendotoxin activity.

Gene transfer with IL-4 and IL-13 improves survival in lethal endotoxemia in the mouse and ameliorates peritoneal macrophages immune competence

Systemic anti-cytokine therapies have been unsuccessful in preventing mortality from gram-negative bacteremia in humans partly because of the failure to neutralize pro-inflammatory cytokines at sites of exaggerated production. In an attempt to deliver anti-inflammatory cytokines to organs directly, gene transfer was employed. Thirty-six BALB/c mice were injected intraperitoneally with cationic liposomes containing plasmids encoding the human interleukin-4 (hIL-4) or IL-13 gene. Both, hIL-4 and hIL-13 mRNA were detected by reverse transcription-polymerase chain reaction analysis in the liver and the spleen of the animals. Fourty-eight hours after the in vivo gene transfer, these 36 mice and 18 mock-transfected mice, were challenged with a lethal dose of E. coli lipopolysaccharide with D-galactosamine (D-GalN). Gene transfer with hIL-4 reduced the serum tumor necrosis factor (TNF)-alpha production in response to endotoxin/D-GalN by 80% from 113.1 pg/ml in mock-transfected animals to 22.2 pg/ml (p < 0.05); human IL-13 gene transfer reduced serum TNF-alpha levels by 90% (113.1 pg/ml to 11.6 pg/ml; p < 0.05). Survival was improved from 20% to over 83% in both treatment groups (p < 0.001). Our data demonstrate a potent in vivo anti-inflammatory action of both IL-4 and IL-13. In addition, the immune functions of peritoneal macrophages are significantly ameliorated in both treatment groups, with IL-13 demonstrating better macrophage immune modulation than IL-4 (p < 0.05).

Biochemical characterization of recombinant fusions of lipopolysaccharide binding protein and bactericidal/permeability-increasing protein. Implications in biological activity

The physiological response to endotoxin (lipopolysaccharide (LPS)) can be regulated by two closely related LPS-binding proteins, LPS-binding protein (LBP), which potentiates LPS' inflammatory activity via interaction with the monocytic antigen CD14, and bactericidal/permeability-increasing protein (BPI), which neutralizes LPS. Both proteins bind LPS with high affinity sites in their N-terminal domains, whereas interaction between LBP and CD14 is dependent upon the LBP C-terminal domain. We have created fusions of the N- and C-terminal domains from each protein and compared the functional activities and pharmacokinetics of these fusions, the individual N-terminal domains, and the parent proteins. The N-terminal domains of BPI and LBP bound lipid A with their characteristic apparent affinity constants, regardless of the C-terminal fusion partner. In addition, the C-terminal domain of LBP allowed transfer of LPS to CD14 in conjunction with either N-terminal LPS binding domain. Proteins containing a BPI N-terminal domain had greater heparin binding capacities in vitro and were cleared more rapidly from the plasma of whole animals. Taken together, these data better define how closely related proteins such as BPI and LBP can have opposing effects on the body's response to LPS.

Antiendotoxin activity of cationic peptide antimicrobial agents

The endotoxin from gram-negative bacteria consists of a molecule lipopolysaccharide (LPS) which can be shed by bacteria during antimicrobial therapy. A resulting syndrome, endotoxic shock, is a leading cause of death in the developed world. Thus, there is great interest in the development of antimicrobial agents which can reverse rather than promote sepsis, especially given the recent disappointing clinical performance of antiendotoxin therapies. We describe here two small cationic peptides, MBI-27 and MBI-28, which have both antiendotoxic and antibacterial activities in vitro and in vivo in animal models. We had previously demonstrated that these peptides bind to LPS with an affinity equivalent to that of polymyxin B. Consistent with this, the peptides blocked the ability of LPS and intact cells to induce the endotoxic shock mediator, tumor necrosis factor (TNF), upon incubation with the RAW 264.7 murine macrophage cell line. MBI-28 was equivalent to polymyxin B in its ability to block LPS induction of TNF by this cell line, even when added 60 min after the TNF stimulus. Furthermore, MBI-28 offered significant protection in a galactosamine-sensitized mouse model of lethal endotoxic shock. This protection correlated with the ability of MBI-28 to reduce LPS-induced circulating TNF by nearly 90% in this mouse model. Both MBI-27 and MBI-28 demonstrated antibacterial activity against gram-negative bacteria in vitro and in vivo against Pseudomonas aeruginosa infections in neutropenic mice.

Protection against endotoxic shock by bactericidal/permeability-increasing protein in rats

Bactericidal/permeability-increasing protein (BPI) is a neutrophil primary granule protein that inhibits effects of LPS in vitro. The current study examined the effects of BPI on hemodynamics, mortality, and circulating endotoxin and cytokines in conscious rats with endotoxic shock. Catheters were implanted into the right femoral artery and vein. 1 d later, human recombinant BPI (10 mg/kg) or vehicle was intravenously injected immediately, 30 min, or 2 h after intravenous injection of LPS (7.5 mg/kg). Mean arterial pressure (MAP) and heart rate were monitored and blood was collected before and after injection. BPI given immediately or 30 min after LPS prevented the LPS-induced reduction in MAP at 4-8 h and markedly reduced mortality. BPI given 2 h after LPS injection had no protective effect. BPI treated immediately after LPS reduced the circulating levels of endotoxin and IL-6 but increased the circulating levels of TNF. We propose that BPI exerts its protective effect through a TNF-independent mechanism, by inhibiting endotoxin-stimulated production of IL-6.

Anti-endotoxin therapy in primate bacteremia with HA-1A and BPI

OBJECTIVE

The in vivo neutralizing activities of an anti-lipopolysaccharide (LPS) antibody HA-1A (Centoxin [Centocor, Malvern, PA]), a human immunoglobulin M monoclonal antibody, and of bactericidal/permeability-increasing protein (BPI), an endogenously produced human LPS-neutralizing protein, were studied in a primate model of lethal Escherichia coli bacteremia.

SUMMARY BACKGROUND DATA

HA-1A has been used with variable success against LPS activity in some animal models and in a recently reported clinical trial. However, no data assessing the efficacy of this agent in subhuman primates is available. Bactericidal/permeability-increasing protein is a product of polymorphomononuclear cells (PMNs) that is stored in azurophilic granules and exhibits LPS-neutralizing activity in vitro and in some in vivo models.

METHODS

Immediately after E. coli infusion and in a blinded fashion, three baboons were treated with BPI (5 mg/kg bolus infusion and 95 micrograms/kg/min infusion over 4 hr). Three animals received 3 mg/kg BW of HA-1A, whereas another three baboons received a placebo treatment.

RESULTS

The BPI-treated animals demonstrated significantly (p < 0.03) lower circulating LPS-limulus amoebocyte lysate (LAL) activity compared with the control animals, but this reduction in LPS-LAL activity was not associated with improved survival. HA-1A treatment did not reduce LPS-LAL activity. However, both BPI and HA-1A treatment did attenuate the pro-inflammatory cytokine response.

CONCLUSION

The current data suggests that incomplete neutralization of endotoxin activity does not alter mortality from severe bacteremia. Given the diversity of mediator production under such circumstances, a strategy of combination therapy in the form of anti-lipopolysaccharide and anticytokine treatment may be necessary to achieve optimal survival.