Are endotoxins and lipopolysaccharides the same?
What are endotoxins?
Bacterial endotoxins (commonly referred to as endotoxins) come from the cell walls of gram-negative bacteria. The endotoxins themselves are molecules with both fat components and complex sugar components. The fat and sugar components of endotoxins are also known as lipopolysaccharides (LPS). Thus, in some cases, endotoxins are also known as lipopolysaccharide endotoxins (LPS endotoxins). Endotoxins can be deadly to humans because they trigger the innate immune system, causing illness. Lipopolysaccharide inflammation is characterized by fever, chills, and septic shock. Endotoxins in sterile injectable drugs at a high enough concentration can cause death via lipopolysaccharide inflammation. If you need endotoxin removal from a sterile injectable via filtration, see our article on depyrogenation HERE.
What is lipopolysaccharide (LPS)?
LPS is the biologically active portion of an endotoxin. LPS is amphipathic and has three distinct regions. The first is a water-repellant (hydrophobic) lipid-A portion that provides lipopolysaccharide’s biological activity. The lipid-A component is essentially the same among Gram-negative bacteria species. The second region is a water-loving (hydrophilic) O-antigen, which varies based on Gram-negative bacteria strain. The final part is an oligosaccharide linkage between the lipid-A and O-antigen potions of LPS.
What is the relationship between endotoxins and lipopolysaccharides (LPSs)?
LPS is a component of an endotoxin, like peanut butter is a component of a peanut butter and jelly sandwich. For this reason, endotoxins are also known as lipopolysaccharide endotoxins. Both the peanut butter and the peanut butter sandwich will cause an allergic reaction. However, the peanut butter sandwich has many more components than the peanut butter alone. The same is true for endotoxins and LPS. Endotoxins have LPS but also have other parts of gram-negative bacteria cells. And while both endotoxins and LPS can cause lipopolysaccharide inflammation and illness in the human body (via high fever), endotoxins and pure LPS are not the same. However, the term LPS, endotoxin, bacterial endotoxin, and lipopolysaccharide endotoxin are often used interchangeably.
How do endotoxins and lipopolysaccharides (LPSs) contaminate medical devices and parenteral products?
Parenteral products and devices are contaminated with endotoxin through Gram-negative bacterial cells or cell wall fragments containing LPS. Gram-negative bacteria frequently populate raw materials and any moist environments. Thus, gram-negative bacteria (and, by extension, endotoxins) can be picked up by sterile products during manufacturing through contact with contaminated surfaces or the use of contaminated raw materials. Lipopolysaccharide’s structure allows it to stick to hydrophobic (water-repellant) and hydrophilic (water-loving) surfaces. Thus, LPS components easily attach to molecules and proteins in solutions or material surfaces, causing endotoxin contamination. LPS also sticks to itself to form LPS chains known as aggregates. Temperature, pH, salt concentration, and other factors affect the biological activity and stability of endotoxins (or purified LPS). A bacterial endotoxin test is the best way to assess the amount of LPS within or attached to a product to prevent lipopolysaccharide inflammation.
What are the similarities and differences between endotoxins and lipopolysaccharides (LPSs)?
LPS and bacterial endotoxins are also known as pyrogens. Pyrogens are molecules or substances that cause a feverous reaction when they enter the human body. Due to their LPS components, Bacterial endotoxins are the most common type of pyrogen. Since endotoxins are fragments of gram-negative cellular walls, they come in many types and sizes. Endotoxins often have more than one LPS structure. In contrast, pure LPS is often a monomer or an aggregation of monomers. Further, unlike endotoxins, purified LPS is not naturally occurring and is laboratory-derived. Due to the differences in structure between purified LPS and endotoxins, one cannot assume that they will have the same adsorptive properties or react the same with different materials or in various liquids (e.g., solutions, emulsions, and suspensions). However, LPS and endotoxins will both cause illness in the human body.
Why is the removal of endotoxin and LPS critical for sterile products?
Medical devices and parenteral products must be sterile and pyrogen-free. Products can accumulate pyrogens from raw materials or other parts of the manufacturing process. Even if a product is sterile, it can still contain pyrogens. Depyrogenation is a process that removes pyrogens. The most prevalent and problematic pyrogens are bacterial endotoxins. The best pyrogen removal or destruction processes are product-dependent. Standard depyrogenation methods are dry heat, rinsing, and filtration. A comparison between depyrogenation via rinsing versus dry heat can be found HERE. Comparisons between endotoxin removal through filtration versus dry heat or rinsing can be found HERE and HERE, respectively.
Summary
Overall, most medical devices, parenteral products, and other health care items must be sterile and pyrogen-free to be used by a patient. Bacterial endotoxins and LPSs are both pyrogens. Bacterial endotoxins (commonly referred to as endotoxins) come from the cell walls of gram-negative bacteria. LPS is the biologically active portion of an endotoxin. Since endotoxins are fragments of gram-negative cellular walls, they come in many types and sizes. Endotoxins often have more than one LPS structure. In contrast, pure LPS is often a monomer or an aggregation of monomers. Further, unlike endotoxins, purified LPS is not naturally occurring and is laboratory-derived. Due to the differences in structure between purified LPS and endotoxins, one cannot assume that they will have the same adsorptive properties or react the same with different materials or in various liquids (e.g., solutions, emulsions, and suspensions). However, LPS and endotoxins will both cause illness in the human body. All in all, ensure you choose a contract testing organization that can provide appropriate sterility and bacterial endotoxin testing for your product needs.
Ethide Labs is a contract testing organization specializing in Sterilization Validations. Ethide Labs also offers Microbiology Testing, Bioburden Testing, Bacterial Endotoxin Testing, EO Residual Testing, Sterility Testing, Cytotoxicity Testing, Environmental Monitoring & Package Integrity Testing services for medical device companies and allied industries. Ethide is an ISO 13485 certified facility.
References
Charles A. Dinarello. Review: Infection, fever, and exogenous and endogenous pyrogens: some concepts have changed. Innate Immunity. August 1, 2004.
Galanos C. and Freudenberg M. A. Bacterial endotoxins: biological properties and mechanisms of action. Mediators of Inflammation. 1993; 2(7): S11–S16.
Michael J. Akers. Sterile Drug Products Formulation, Packaging, Manufacture, and Quality. Drugs and the Pharmaceutical Sciences. Informa Healthcare. 2010.
United States Pharmacopeial Convention. <85> Bacterial Endotoxins Test. Rockville, MD, USA. 2021. (USPC <85>).
United States Pharmacopeial Convention. <1211> Sterility Assurance. Rockville, MD, USA. 2021. (USPC <1211>).
United States Pharmacopeial Convention. <1228.5> Endotoxin Indicators For Depyrogenation. Rockville, MD, USA. 2021. (USPC <1228.5>).
