Bacterial membranes lipopolysaccharides

Huang etal. (2002) prepared an antibody array for the simultaneous detection of 43 cytokines. They were able to verify the down-regulation of MCP-1 cytokine in transfected cells (human glioblastoma cells transfected with cx43 expression vector) relative to control cells. The antibody array is an emerging technology. In at least one study based upon the use of a commercial membrane format, the cytokine microarray failed to accurately determine cytokine levels in bacterial and lipopolysaccharide (LPS)-stimu-lated whole human blood (Copeland, 2004). 

Polymers having carbohydrate chains linked to a lipid anchor embedded in a bacterial membrane the term bacterial amphiphiles was suggested5 for these polymers. Lipopolysaccharides of Gram-negative bacteria constitute the best-known example of these polymers. 

Solid supported bilayers of other composition have also been reported such as lipopolysaccharide bilayers which can mimic the outer bacterial membrane with this example used to monitor bacteriophage interaction by AFM [81]. 

Another interesting antibiotic constmct is a peptide-conjugated form of j8-KDO. jS-KDO is an inhibitor of the CMP-KDO synthetase that is involved in lipopolysaccharide (LPS) synthesis, a major constituent of the bacterial cell wall. Antibacterial activity is thus accomplished by interference with cell wall construction. /3-KDO is incapable of membrane permeation, and therefore is not useful as an antibiotic in its native form. Hammond et al. have shown that conjugation of a /3-KDO analog to certain dipeptides resolves this problem [184] (O Fig. 14). Attachment of the /3-KDO analog to a dipeptide allows the glycopeptide constmct to permeate the bacterial membrane. Inside the cell, proteases hydrolyze the peptide and release the inhibitor, resulting ultimately in bacterial cell death. 

The multi-hit hypothesis has also been used to explain the immunological potentiation of some idiosyncratic DILI. In this scenario, a preexisting inflammation in the host serves as "first hit." The drug treatment serves as "second hit." A good animal model for this scenario is rodents pretreated with bacterial membrane preparations such as lipopolysaccharide (LPS), followed by drug treatment. This model has been applied to explain idiosyncratic DILI caused by antibiotics, where the intended patients typically experience preexisting inflammation caused by bacterial infection.68-71... 

In Gram-negative bacteria the cell wall is only about 3 nm thick, and located in the extended periplasmatic space between the inner membrane (IM) and an additional outer membrane (OM). The lipid monolayer in the outer leaflet of the OM contains about 90% lipopolysaccharides (LPS). LPS consist of Lipid A and an oligosaccharide component, which is highly specific for individual bacterial species and phenotypes [108, 114]. 

Carbohydrates related to membranes can be found as lipopolysaccharides or as parts of glycoproteins. Sugars are often characteristic determinants of cell surfaces (see below). The great majority of carbohydrates are found in the outer leaflet of a membrane, resulting in an asymmetrical structure. This is especially true for many plasma membranes and the outer membrane of Gram-negative bacterial cells (see below). 

Chemical nature Lipopolysaccharide (LPS), component of the bacterial outer membrane Proteins... 

Endotoxins are bacterial cell envelope constituents that, when present in pharmaceutical products, cause pyrogenic reactions sometimes resulting in lethality. The toxicity of endotoxins is directly related to their chemical composition. However, the viability of the organism is irrelevant since endotoxin derived from dead or live microbes is equally active. The classical endotoxin is lipopolysaccharide (LPS). However, peptidoglycan (PG) also displays endotoxin-like activities. LPS is found only in gram-negative bacterial outer membranes, while PG is present in the cell... 

Lipopolysaccharides are the dominant surface feature of the outer membrane of gram-negative bacteria such as Escherichia coli and Salmonella ty-phimurium. These molecules are prime targets of the antibodies produced by the vertebrate immune system in response to bacterial infection and are therefore important determinants of the serotype of bacterial strains (serotypes are strains that are distinguished on the basis of antigenic properties). The lipopolysaccharides of S. typhimurium contain six fatty acids bound to two... 

FIGURE 7-32 Bacterial lipopolysaccharides. (a) Schematic diagram of the lipopolysaccharide of the outer membrane of Salmonella ty-phimurium. Kdo is 3-deoxy-o-manno-octulosonic acid, previously called ketodeoxyoctonic acid Hep is L-glycero-D-mannoheptose AbeOAc is abequose (a 3,6-dideoxyhexose) acetylated on one of its hydroxyls. There are six fatty acids in the lipid A portion of the molecule. Different bacterial species have subtly different lipopolysaccharide structures, but they have in common a lipid region (lipid A), a core oligosaccharide, and an "O-specific" chain, which is the prin-... 

In bacterial lipopolysaccharides, O-specific chains composed of repeating, or modified repeating, units are linked to a unique oligosaccharide sequence of the core region which is connected to a lipid A fragment serving as a hydrophobic anchor embedded in the bacterial outer-membrane. Biosynthesis of O-specific chains was found to occur independently on formation of other structural fragments of the lipopolysaccharide molecule. Both block and monomeric mechanisms were demonstrated for the biosynthesis of these polymers. 

An important role in the nonspecific cellular response is played by Paneth cells which line the bottom of the intestinal glands. Their granules contain compounds that can damage bacteria. These include a lysozyme which damages peptidoglycan, the basic structure of Gram positive bacterial cellular membrane secreted phospholipase A2 involved in lipopolysaccharide metabolism and a-defensins, cryptydins, which decompose bacterial proteins. 

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