Evaluation of lipopolysaccharide aggregation by light scattering spectroscopy

Lipopolysaccharides (LPS) are cell wall components of Gram-negative bacteria. These molecules behave as bacterial endotoxins and their release into the bloodstream is a determinant of the development of a wide range of pathologies. These amphipathic molecules can self-aggregate into supramolecular structures with different shapes and sizes. The formation of these structures occurs when the LPS concentration is higher than the apparent critical micelle concentration (CMC(a)). Light scattering spectroscopy (both static and dynamic) was used to directly characterize the aggregation process of LPS from Escherichia coli serotype 026:B6. The results point to a CMC(a) value of 14 microg mL(-1) and the existence of premicelle LPS oligomers below this concentration. Both structures were characterized in terms of molecular weight (5.5 x 10(6) and 16 x 10(6) g mol(-1) below and above the CMC(a), respectively), interaction with the aqueous environment, gyration radius (56 and 105 nm), hydrodynamic radius, (60 and 95 nm) and geometry of the supramolecular structures (nearly spherical). Our data indicates that future in vitro experiments should be carried out both below and above the CMC(a). The search for drugs that interact with the aggregates, and thus change the CMC(a) and condition LPS interactions in the bloodstream, could be a new way to prevent certain bacterial-endotoxin-related pathologies.