Definition
Lipopolysaccharide from Gram-negative bacteria that can confound cell and animal studies; measured by the LAL test.
Endotoxins are lipopolysaccharides from the outer membrane of Gram-negative bacteria. They are heat-stable, survive lyophilisation and are not removed by standard sterile filtration. Even trace levels can activate innate immune signalling, such as Toll-like receptor 4 pathways, producing inflammatory responses in cell culture and animal models that may be mistaken for an effect of the peptide. Endotoxin is measured by the Limulus amebocyte lysate (LAL) test described in USP ⟨85⟩ and reported in EU/mg. Not every research-grade certificate of analysis includes an endotoxin result, so researchers working with immune cells or in vivo models often request one for each batch.