The preparation of a lipidic endotoxin affects its biological activities

Abstract

Bacterial membrane constituents, such as Ornithine-containing lipid (OL) and the lipid A portion of lipopolysaccharide, trigger various immune responses through recognition by Toll-like receptor (TLR) 4. Usually, these lipids are dissolved in a small amount of aqueous or organic solvent before being added to the culture medium for examination of their biological activities. Macrophages stimulated with OL or lipid A sonically dissolved in saline released both interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). In contrast, macrophages stimulated with OL or lipid A sonically dissolved in ethanol or dimethyl sulfoxide (DMSO) secreted much TNF-α, but very little EL-1β. These results, taken together, indicate that how an endotoxin is prepared affects its biological activities. In addition, electromicroscopic analysis revealed that sonication of air-dried OL or lipid A in DMSO produced larger particles than those produced in saline, suggesting that the process of preparing lipidic TLR4-ligands affects their physical state including particle size, and that the physical state might be an important determinant of biological activity. © 2008 Pharmaceutical Society of Japan.