title: Polymyxin B antagonizing biological activity of lipopolysaccharide.
abstract: 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-alpha and IL-6 in murine peritoneal macrophages a (PMphi) after exposure to LPS (100 ng/ml) were detected, and the expression levels of TLR4, TNF-alpha and IL-6 mRNA in PMphi 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 nmol/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-alpha and IL-6 mRNA and the release of cycokines in LPS-stimulated murine peritoneal macrophages.
  
  
  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.
authors.affiliation: Medical Research Center, Southwest Hospital, Third Military Medical University, Chongqing 400038, China.
authors.forename: Yi-bin
authors.initials: YB
authors.lastname: Guo
authors.forename: Li-ping
authors.initials: LP
authors.lastname: Chen
authors.forename: Hong-wei
authors.initials: HW
authors.lastname: Cao
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.forename: Jiang
authors.initials: J
authors.lastname: Zheng
authors.forename: Guang-xia
authors.initials: GX
authors.lastname: Xiao
mesh_terms: D000818:Animals; D016207:Cytokines / Q000032:analysis; D008033:Limulus Test; D008050:Lipid A / Q000037:antagonists & inhibitors; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors*; D008264:Macrophages / Q000737:chemistry; D051379:Mice; D011112:Polymyxin B / Q000494:pharmacology*
chemical_list: D016207:Cytokines; D008050:Lipid A; D008070:Lipopolysaccharides; D011112:Polymyxin B