Polymyxin B antagonizing biological activity of lipopolysaccharide

Objective: To investigate the mechanism of polymyxin B (PMB) antagonizing the biological activity of lipopolysaccharide (LPS). Methods : The affinity of PMB for LPS and lipid A was assayed by biosensor, and the neutralization of PMB for LPS (2 ng/ml) was detected by kinetic turbidimetric limulus test. The releases of TNF-α and IL-6 in murine peritoneal macrophages (PMφ) after exposure to LPS (100 ng/ml) were detected, and the expression levels of TLR4, TNF-α and IL-6 mRNA in PMφ induced by LPS (100 ng/ml) were measured by RT-PCR. Results: PMB had high-affinity to LPS and lipid A with dissociation equilibrium constants of 18.9 nmo/L and 11.1 nmol/L, respectively, and neutralized LPS in a dose-dependent manner. Furthermore, PMB could markedly inhibit the expressions of TLR4, TNF-α and IL-6 mRNA and the release of cycokines in LPS-stimulated murine PMφ. Conclusions: PMB neutralizes LPS and inhibites the expression and release of cycokines in macrophages, in which the affinity of PMB for lipid A plays an important role.