Protein-free lipopolysaccharides

Some polymyxins are sold for second-line systemic therapy. Polymyxin B sulfate and colistimethate sodium can be used for intravenous, intramuscular, or intrathecal administration, especially for Pseudomonas aerupinosa mP QXiosis, but also for most other gram-negative organisms, such as those resistant to first-line antibiotics. Nephrotoxicity and various neurotoxicities are common in parenteral, but not in topical, use. Resistance to polymyxins develops slowly, involves mutation and, at least in some bacteria, adaptation, a poorly understood type of resistance that is rapidly lost on transfer to a medium free of polymyxin. Resistance can involve changes in the proteins, the lipopolysaccharides, and lipids of the outer membrane of the cell (52). Polymyxin and colistin show complete cross-resistance. 

Incubation periods in excess of 2 h were required before this activity was detected in cell-free supernatants. More recently, the use of cDNA probing of Northern transfers (to detect specific mRNA levels), the use of ELISA techniques (to detect protein levels immunologically) and the development of more specific bioassays (culture techniques in which a biomolecule stimulates proliferation in a particular cell line) have resulted in a more thorough analysis of IL-1 production by neutrophils. IL-1 is only poorly expressed in blood neutrophils because mRNA for this cytokine is detectable only at very low levels (if at all), and protein production is usually below the level of detection of most assays. However, exposure of neutrophils to lipopolysaccharide (LPS), or to cytokines such as GM-CSF, TNF or IL-1 itself, results in a rapid but transient increase in IL-1 expression. 

Naturally occurring bacterial endotoxins contain the lipid, carbohydrate, and protein makeup of the outer cell membrane of GNB (Fig. 1). However, most of the commercial endotoxin preparations have been purified by various extraction procedures and are generally free of nucleic acids, proteins, phospholipids, and other bacterial cell components. The primary chemical configuration that remains after purification is apolysaccharide structure that is covalently bound to a lipid component called Lipid A. Based on its chemical nature, which is common to various bacterial families, this substance is referred to as lipopolysaccharide (LPS). Although the terms endotoxin and LPS are often used interchangeably, most reference endotoxin standards are purified preparations that are more correctly described as LPS. 

Pu, Y., McCormick, C.C., Roneker, C., and Lei, X.G. (2001). Lipopolysaccharide and interferon-gamma-induced nitric oxide production and protein oxidation in mouse peritoneal macrophages are affected by glutathione peroxidase-1 gene knockout. Free Radic Biol Med 31, 450-9. 

---