Sepsis is a life-threatening health condition characterized by bacterial infection with a strong inflammatory response. The response from our innate immune system to the bacteria releases the inflammatory products and mediators which subsequently causes the pathogenesis of sepsis. A major component responsible for the inflammation is lipopolysaccharide (LPS), mostly found in the outer membrane of gram-negative bacteria, which also contributes significantly to the structural integrity of the gram-negative bacteria. The interaction of LPS with membrane lipids is therefore very important to understand the mechanisms of LPS recognition through the cell membrane. Most part of the outer membrane of the eukaryotic cell membrane is composed of phosphatidylcholine (PC) where the presence of cholesterol is known to play a vital biophysical role in maintaining lipid-packing density and membrane fluidity. Our focus here is to study the monolayers of common phosphatidylcholine (DMPC) along with cholesterol as a model membrane system and investigate their interactions with LPS using Langmuir-Blodgett (LB) method and atomic force microscopy (AFM). Also, the interactions between these model membranes along with LPS and a potential LPS-antagonist, AM-12, will be examined. The LPS-antagonist, AM-12, is a lipid A analog containing a glucopyranoside core, hydrophobic ether substituents, and an amino acid, which has been shown to be an effective inhibitor of LPS-induced tumor necrosis factor-alpha (TNF-α) production in human macrophages. The surface pressure–area isotherm obtained by the LB method is very helpful for investigating the phase transitions of the monolayers at different surface pressures and molecular areas. Surface compressional modulus also can be calculated using these surface pressure–area data to observe the physical states of the monolayers. After transferring these monolayers onto a solid substrate, the AFM was used to study their surface structures, mechanical properties, and interactions.

Monolayer study of DMPC, cholesterol and their interactions with LPS and a potential LPS-antagonist; AM-12

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