The Influence of Chitosan on the Ability of LPS to Interact with Cells of the Immune System

Complexes of lipopolysaccharide (LPS) from the bacterium Escherichia coli and chitosan (CN) with a molecular weight of 5 kDa were obtained and their supramolecular organization was studied. Using atomic force microscopy, it was shown that during the formation of complexes there is a transition from the micellar structure of the original LPS to linear network structures uniformly distributed over the surface of mica. The stability of LPS-CN complexes of various stoichiometries in biological media in the presence of serum proteins was investigated. It was shown that complexes with an LPS–CN ratio of 1 : 1 in the presence of serum proteins lost their surface charge and tended to aggregate while complexes with the maximum saturation of CN (1 : 5) did not aggregate under these conditions and maintained their surface charge. The effect of CNs of different molecular weights on the ability of LPS to interact with neutrophils of human whole blood was studied. It was observed that LPS-CN complexes were capable of binding to neutrophils and internalazing the cell, and this ability was enhanced in the presence of serum proteins. Chitosan exhibited the ability to suppress the synthesis of the proinflammatory cytokine TNF-α induced by LPS, not only as part of the complex but also when cells were pretreated with a polycation.