Bactericidal and endotoxin neutralizing activity of a peptide derived fromLimulus antilipopolysaccharide factor

Background. Release of lipopolysaccharide (endotoxin, LPS) is a critical in citing event in the development of sepsis syndrome due to gram-negative bac teria, and mortality associated with this entity remains similar to 40 %. L imulus anti-LPS factor (LALF) is a naturally occurring horseshoe crab deriv ed protein that, unlike antibiotics, is both bactericidal for gram-negative bacteria and capable of neutralizing LPS. We hypothesized that a peptide d erived from the active domain of LALF (LALF #28-54) would exhibit potent bi ologic activity similar to that of LALF itself and could potentially be use ful as a therapeutic agent. Methods. The effects of LALF, synthetic peptide LALF #28-54, polymyxin B (P mB), and a biologically inactive synthetic peptide were examined in several models. In vitro bactericidal activity was determined against Pseudomonas aeruginosa, and LPS-neutralizing capacity was determined via inhibition of LPS-induced tumor necrosis factor-alpha (TNF-alpha) secretion by RAM 264.7 cells. In vivo biologic activity was determined via pretreatment following which P aeruginosa endotoxemia or bacteremia was induced; serum TNF-alpha l evels, bacterial clearance, and survival were assessed. Results. LALF and LALF #28-54 exhibited potent in vitro bactericidal and LP S-neutralizing activity comparable to PmB (P < .01). However, although LALF #28-54 diminished systemic TNF-alpha production and aided bacterial cleara nce similar to that observed for LALF (P < .01), it did not provide signifi cant protective capacity (P > .1). Conclusions. These data demonstrate that peptide LALF #28-54 retained the L PS-neutralizing and bactericidal biologic activity of LALF but failed to pr otect during overwhelming P aeruginosa bacteremia, perhaps due to short ser um half-life.