Protection of mice from mortality caused by living and heat-killed bacteria by SDZ MRL 953.

Protective effects of SDZ MRL 953, a monosaccharidic lipid A analog with a reduced toxicity, were investigated in models of experimental septic shock caused by injections of LPS, and inoculations of heat-killed or live bacteria. Female B6D2F1 mice were challenged with a combination of galactosamine (800 mg/kg) plus various doses of heat-killed isolates of Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, and Staphylococcus aureus or LPS from Salmonella abortus equi. In some experiments, isolates of living bacteria at sublethal inocula were also combined with galactosamine. More than 90% of the animals died within 24 hr when the challenge was performed either simultaneously with or up to 4 hr after an intraperitoneal administration of galactosamine. No death was observed when galactosamine was omitted or administered after the microbial or LPS challenge. Pretreatment of the animals with SDZ MRL 953 (1-10 mg/kg) rendered the animals resistant to the lethal effects of both bacterial and LPS challenge in a time- and dose-dependent manner. The levels of TNF-alpha in control mice rose to greater than 600 pg/ml 2 hr postbacterial or LPS challenge, but were below detection in animals pretreated with SDZ MRL 953. Protection against both the infection and the toxicity of heat-killed bacteria or LPS was also achieved when murine anti-TNF-alpha monoclonal antibody was administered prophylactically. Together, these data suggest that SDZ MRL 953 enhances the resistance of mice against the toxicity of heat-killed gram-negative bacteria and S. aureus, and attenuates host responses to living bacteria which may lead to irreversible shock and death.