Considerable evidence now supports the experimental findings that penicillin-binding protein (PBP)-2 specific antimicrobial agents such as imipenem generate less endotoxin than PBP-3 specific agents such as ceftazidime during the process of bacteriolysis of Gram-negative bacteria. To determine if differences in endotoxin release have pathophysiologic significance in vivo, Sprague-Dawley rats were experimentally challenged with intraperitoneal injections of virulent, serum-resistant clinical strains of the following Gram-negative bacilli: Escherichia coli 018:K1, Klebsiella pneumoniae K2, and Pseudomonas aeruginosa 12.4.4 (immuno type 6). After intravenous administration of imipenem (25 mg/kg), ceftazidime (50 mg/kg) or saline control, imipenem and ceftazidime-treated animals had rapid reductions in the quantitative level of bacteremia from all three pathogens. Peritoneal fluid samples revealed spherical forms with imipenem and long, filamentous forms with ceftazidime. Circulating plasma endotoxin levels were consistently higher ( P < 0.05) with ceftazidime than imipenem for 6 h after administration of E. coli or P. aeruginosa intraperitoneal challenge. Endotoxin levels were unchanged to slightly higher with imipenem than ceftazidime following K. pneumoniae intraperitoneal challenge. TNF levels peaked 2 h post-therapy and were consistently higher with ceftazidime-treated animals ( P < 0.05). D-galactosamine-treated animals had LD50 values that were 0.5-2 log higher ( P < 0.001) with imipenem for E. coli and P. aeruginosa but did not differ from ceftazidime in animals challenged with the K. pneumoniae strain. These results indicate that the PBP-2 specific agent imipenem led to significantly less endotoxin release than did ceftazidime with its great affinity to PBP-3. Differential endotoxin release was found after antimicrobial therapy with the E. coli and P. aeruginosa strains but not with the K. pneumoniae strain tested in this study. The clinical relevance of these findings with treatment of systemic Gram-negative infections in humans will require further clinical investigation.

A chimeric protein consisting of the N-terminal domain of lipopolysaccharide-binding protein and the C-terminal domain of bactericidal/permeability-increasing protein demonstrated a dose-dependent survival benefit (P ‫؍‬ 0.001) and reduced endotoxin levels (P < 0.01) in neutropenic rats with Pseudomonas aeruginosa sepsis. This lipopolysaccharide-binding protein-bactericidal/permeability-increasing peptide has favorable pharmacokinetics and antiendotoxin properties which may be of value for human sepsis.Current therapeutic options for gram-negative bacterial sepsis are limited to antimicrobial agents, hemodynamic support, and management of sepsis-induced organ dysfunction (4). Efforts to interfere directly in the pathophysiologic mechanisms which underlie the septic process have yielded inconsistent and largely disappointing results. Antiendotoxin monoclonal antibodies (11, 18), anticytokine therapies (1,6,8), and other anti-inflammatory strategies (5, 24) have not proven to be of sufficient benefit to warrant approval as standard adjunctive therapies for human sepsis.Despite these setbacks, it is anticipated that refinements in clinical trial design and innovations in the synthesis of more potent therapeutic agents will lead to significant advances in the treatment of sepsis in the future. A naturally occurring endotoxin-binding and neutralizing protein which may prove to be particularly effective in endotoxemic states is bactericidal/ permeability-increasing protein (BPI) (17,25). This cationic human neutrophil-derived, 456-amino-acid protein is known to possess potent endotoxin neutralizing properties and intrinsic antimicrobial actions (16,20,26). It has recently been shown that BPI is protective in a variety of endotoxin challenge experiments both in vitro (3, 9, 19) and in vivo (2, 7, 16).A potential limitation to the therapeutic utility of BPI in clinical endotoxic shock is its rapid clearance from the central circulation, with a plasma half-life of only 2 to 4 min in experimental animals (7). A recombinant fusion construct of human BPI with a closely related endotoxin-binding protein, known as lipopolysaccharide (LPS)-binding protein (LBP) (23, 27), has been generated; this combines the endotoxin-neutralizing properties of BPI with the favorable clearance properties of LBP. BPI and LBP are genetically (10) and structurally (26) related proteins, yet they have opposing physiologic actions in the presence of LPS (12,22). BPI inhibits interactions between LPS and CD14-bearing effector cells such as neutrophils and monocytes. LBP, in contrast, facilitates the delivery of LPS to CD14 antigens on cell membranes and potentiates LPS activity.A chimeric protein consisting of the first 199 amino acids of the amino terminus of LBP and the C-terminal 257 amino acids of BPI was found to possess desirable attributes of both LBP and BPI in endotoxin challenge models (15). This fusion peptide was tested in a bacteremic infection model of Pseudomonas aeruginosa sepsis in neutropenic rats.(This paper was presented in part ...