Endotoksinit

Endotoxins, also called lipopolysaccharides (LPS), are large molecules that constitute an essential component of the outer membrane of Gram‑negative bacteria such as Escherichia coli, Salmonella and Pseudomonas. Each endotoxin consists of a lipid A domain, a core oligosaccharide and an O‑antigen polysaccharide. The lipid A portion is mainly responsible for the biological activity and usually contains phosphates and fatty acid chains that anchor it in the bacterial membrane.

When a Gram‑negative cell dies or lyses, endotoxin can be released into the surrounding environment. In the host organism, the lipid A portion binds to Toll‑like receptor 4 on immune cells. This activates intracellular signalling cascades that lead to the release of inflammatory cytokines, such as interleukin‑1, interleukin‑6, tumour necrosis factor‑α and interferon‑γ. The resulting systemic inflammatory response can manifest as fever, chills, hypotension and, in severe cases, septic shock.

Endotoxin potency is measured by its toxic equivalence units (TEU), reflecting the concentration required to elicit a specific biochemical response. Because endotoxin can trigger a strong inflammatory reaction even at low concentrations, its presence in pharmaceuticals, medical devices and vaccines is strictly regulated. The European Pharmacopoeia, United States Pharmacopeia and World Health Organization provide standardized test methods, such as the Limulus amebocyte lysate (LAL) assay, to detect and quantify endotoxin.