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Department of Pulmonology, University of Limburg, Maastricht, Netherlands.In this study, the release of bactericidal/permeability-increasing protein (BPI), which is stored in polymorphonuclear leukocytes (PMNL), was analyzed in a whole blood ex vivo system. Of the microbial products tested, lipopolysaccharide (LPS) most potently induced BPI release; FMLP, serum-treated zymosan (STZ), and lipoteichoic acid (LTA) also induced BPI release. In addition, the inflammatory mediator tumor necrosis factor (TNF)-alpha potently activated PMNL in whole blood, via TNF receptor p55, to release BPI, whereas interleukin (IL)-1, IL-8, platelet activating factor, and C5a were poor inducers of BPI release. STZ and phorbol myristate acetate, but not LPS, FMLP, or LTA, stimulated isolated PMNL to release BPI. BPI was released in comparable magnitude with the azurophilic granule protein elastase. Furthermore, both proteins were released with similar kinetics, which started within 30 min after onset of stimulation and lasted 1-4 h.

The toxicity of lipopolysaccharide (LPS) is modified by several proteins, such as bactericidal/permeability-increasing protein (BPI) and LPS-binding protein (LBP). BPI and LBP plasma levels were measured in patients with gram-negative (n = 36) or gram-positive (n = 28) bacteremia. Levels of BPI and LBP, which are proteins that neutralize and enhance LPS effects, respectively, were increased before bacteremia was first detected. The BPI/neutrophil ratio, reflecting neutrophil activation, was significantly associated with the presence of sepsis syndrome and death in bacteremic patients: 1.06 (0.11-6.49) versus 0.57 (0.06-3.82) in patients with and without sepsis syndrome (P < .01), respectively, and 0.64 (0.06-3.82) versus 1.02 (0.12-6.49) in survivors and nonsurvivors (P < .05), respectively (ratio in nanograms of BPI per 10(6) neutrophils). High LBP peak levels were significantly associated with the presence of sepsis syndrome (P < .01). No differences in BPI and LBP levels were observed in patients with gram-negative versus gram-positive bacteremia. BPI/neutrophil ratio, as a parameter of neutrophil activation, may be useful in monitoring infectious disease.

Endotoxin triggers the subarachnoid inflammation of gram-negative meningitis. This study examined the ability of a recombinant N-terminal fragment of bactericidal/permeability-increasing protein (rBPI23) to block endotoxin-induced meningitis in rabbits. Intracisternal (ic) injection of 10-20 ng of meningococcal endotoxin induced high cerebrospinal fluid (CSF) concentrations of tumor necrosis factor (TNF) and CSF pleocytosis and increased CSF lactate concentrations. ic administration of rBPI23 significantly reduced meningococcal endotoxin-induced TNF release into CSF (P < .005), lactate concentrations (P < .001), and CSF white blood cell counts (P < .01). No such effect was observed in animals receiving intravenous rBPI23. Concentrations of rBPI23 in CSF were high after ic administration but low or undetectable after systemic administration. Thus, high concentrations of rBPI23 can effectively neutralize meningococcal endotoxin in CSF, but low CSF concentrations after systemic administration currently limit its potential usefulness as adjunctive drug treatment in gram-negative meningitis.

Bactericidal/permeability-increasing protein (BPI) has bactericidal properties and also binds lipopolysaccharide (LPS). The ability of a recombinant amino-terminal fragment of BPI to protect mice from death after challenge with a number of different strains of Escherichia coli was tested. BPI prevented death in animals challenged with the J5 rough strain but not with smooth strains O111:B4 and O7K1. Protection was associated with a reduction in serum LPS and tumor necrosis factor-alpha levels but not with reduction in blood bacterial counts. BPI was effective at protecting against death in mice injected with purified O111:B4 LPS. Lack of protection after injection with live O111:B4 and O7K1 may be due to production by these models of approximately 1000-fold higher blood bacterial count compared with J5. Thus, BPI is a promising therapy in the treatment of gram-negative septic shock, although the range of organisms against which it is effective remains to be determined.

Effects of an N-terminal fragment of bactericidal/permeability increasing protein (rBPI21) on bacterial infections were determined. Intravenous (i.v.) rBPI21 increased survival and reduced bacteremia in rats after an iv injection of Escherichia coli O7:K1 bacteria. rBPI21 inhibited the rise in tumor necrosis factor-alpha resulting from challenge with 2 strains of E. coli. Intraperitoneal (ip) injection of rBPI21 increased survival of mice after ip injection of E. coli O7:K1 and Pseudomonas aeruginosa and reduced bacteria in peritoneal lavage fluid and blood and inhibited cytokine production in response to E. coli. rBPI21 alone did not protect mice challenged with E. coli O111:B4 but was protective and reduced bacterial counts when administered in combination with the antibiotic cefamandole. The data show that protection with rBPI21 is associated with reductions in bacterial counts and is enhanced by antibiotics. Bactericidal activity, in addition to antiendotoxin activity, is involved in the efficacy of rBPI21 in models of gram-negative infection.

Characterization of two monoclonal antibodies directed against bactericidal/permeability-increasing protein.Dentener MA, Smit FT, Francot GJ, Buurman WA.Department of Surgery, University of Limburg, Maastricht, Netherlands.In this study the production and characterization of two monoclonal antibodies (MAbs), 4E3 and 5D7, against the bactericidal/permeability-increasing protein (BPI) were described. Using ELISAs, both 4E3 and 5D7 were shown to detect recombinant (r) BPI. Furthermore, natural BPI present in polymorphonuclear leukocytes (PMNL) was detected by both 4E3 and 5D7. The use of both MAbs in flow cytometry revealed that PMNL expressed low levels of cell-surface BPI. Lipopolysaccharide (LPS) was shown to block the interaction between anti-BPI MAb and rBPI. In addition, the MAbs blocked biologic activity of rBPI. The inhibition by BPI of LPS activation of the limulus amebocyte lysate assay and of LPS-induced tumor necrosis factor-alpha release by monocytes was prevented by 4E3 and 5D7. Both MAbs are specifically directed against BPI and can inhibit BPI bioactivity

A recombinant (r) NH2-terminal fragment of bactericidal/permeability-increasing protein, rBPI23, was shown to inhibit murine macrophage nitric oxide (NO) production elicited by lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma). Normal mouse plasma amplified NO synthesis (measured as NO2- release) at LPS concentrations of 1-10 ng/mL, and antibody to the plasma LPS-binding protein (LBP) partially inhibited NO2- release in the presence of normal mouse plasma. rBPI23 (1 microgram/mL) effectively inhibited LPS-dependent NO2- release in the presence or absence of normal mouse plasma. Fifty percent inhibition of IFN-gamma/LPS-elicited NO2- production or of binding of fluoresceinated LPS was obtained with approximately 0.2 microgram/mL rBPI23. These results provide a basis for studies of rBPI23 effects on NO synthase activity in murine models of gram-negative sepsis.

Bactericidal/permeability-increasing protein (BPI), a cationic protein found in neutrophil granules, binds with high affinity to gram-negative bacterial lipopolysaccharide (LPS) and can inhibit its actions in vitro. The in vivo efficacy of a recombinant 23-kDa amino-terminal LPS-binding fragment of BPI (rBPI23) was assessed in a mouse model of lethal endotoxemia. Systemic administration of rBPI23 protected actinomycin D-sensitized mice from lethal LPS (Escherichia coli O111:B4) challenge in a dose-dependent manner, with almost complete protection at the highest dose (10 mg/kg; 93% survival vs. 13% in vehicle-treated controls). Surviving rBPI23-treated animals did not show histopathologic signs of tissue damage evident in control animals that had died after LPS challenge. rBPI23 also attenuated the LPS-induced elevation in serum levels of tumor necrosis factor-alpha and interleukin-1 alpha, mediators believed to be involved in the pathogenesis of endotoxemia and sepsis. Thus, rBPI23 may be a potential new therapeutic agent for the treatment of gram-negative bacterial infection and sepsis.