The Structure of Endotoxin and Its Removal Method by Membrane Filtration

Endotoxin is a heat-stable toxic substance that can usually withstand commonly used sterilization temperatures, such as dry heat or autoclaving, and can withstand temperatures up to 250°C for a short period of time without significant degradation, so only by Traditional heating methods are not sufficient to eliminate endotoxins, which are associated with the outer membrane of some types of Gram-negative bacteria, which are part of the bacterial cell wall and can be released when the bacteria lyse or divide. From a chemical point of view, endotoxins It is a type of lipopolysaccharide (LPS), composed of lipids and polysaccharides linked by covalent bonds.

The molecular structure of endotoxin (LPS) consists of three main parts:

O-Bacteria-specific polysaccharide: This is an outwardly extending polysaccharide chain, the outermost part of LPS, composed of repeating units of oligosaccharides, which may be different in different types of bacteria, O antigen in Bacterial strains vary widely among strains and play a role in bacterial recognition and immune response.

Non-specific core polysaccharide: This region connects lipid A and O antigens, the structure of which is different for different species of bacteria, and its presence contributes to the immunogenicity of LPS.

Lipid A: This is the endotoxin portion of the LPS molecule, which is embedded within the bacterial outer membrane.

Endotoxin, especially lipid A, can trigger a strong immune response in humans and animals. When released into the blood during bacterial infection or cell lysis, it binds to Toll-like receptor 4 (TLR4) on immune cells, triggering A cascade of inflammatory responses that leads to the release of pro-inflammatory cytokines, activation of immune cells, and systemic effects such as fever, hypotension, and organ dysfunction.

There are several commonly used methods to remove or reduce endotoxin levels, such as filtration, adsorption, chemical treatment, high-temperature treatment, etc. Here we mainly introduce the method of microporous membrane filtration.

Lipid A in endotoxin is the most conserved structure of LPS among bacterial species, it is mainly responsible for the toxic activity of endotoxin, it consists of a highly acylated and phosphorylated disaccharide backbone, due to the presence of phosphate and carboxyl groups, endotoxin With a net negative charge, it will affect the solubility of molecules, the interaction with other molecules and the recognition of immune cells. From the perspective of membrane filtration to consider the elimination of endotoxins, you can choose a filter membrane with a positive charge.

Some conventional filter membranes can remove bacteria, but not the endotoxins they release, only

Ultrafiltration membranes with a molecular weight cut-off (MWCO) smaller than the size of endotoxins can be used to remove endotoxins from solutions. In addition, nanofiltration and reverse osmosis membranes can also be used due to their smaller pore sizes. If positively charged micropores are used The filter membrane is a more suitable choice. On the one hand, it can intercept through the pore size, and it can also use the adsorption function to remove endotoxin.

Removing endotoxins from solutions, especially those used for medical or pharmaceutical purposes, is a complex task that is carried out under controlled conditions. To ensure complete removal of these potentially harmful substances, the most sophisticated filtration is often used method, or a combination of various measures, in order to achieve the best results.