Bacterial Endotoxin vs. Cytotoxicity Testing
What is an endotoxin?
The “endo” in endotoxin refers to something that is within. The “toxin” component of endotoxin relates to something poisonous. Endotoxins can be deadly to humans and come from the cell walls of gram-negative bacteria. The endotoxins themselves are molecules with fat components (lipids) and complex sugar components (also known as polysaccharides). The fat and sugar components of endotoxins are why endotoxins are also known in scientific literature as lipopolysaccharides (LPS). Endotoxins are also considered pyrogens because they trigger the innate immune system and produce fever when released within the human body.
What is cytotoxicity?
The “cyto” in cytotoxicity stands for cell. The “toxic” component of cytotoxicity refers to something poisonous. Thus, cytotoxicity refers to molecules and compounds that are poisonous to living cells. Cytotoxins are often chemical but can also be from natural or biological sources.
Are endotoxins cytotoxic?
Endotoxins can cause cytotoxic effects when they activate a patient’s immune system. However, it is unclear if endotoxins are toxic to cells without the addition of an immune reaction (Nalbantsoya et al. and Kessel et al.).
What are the differences between endotoxins and cytotoxicity?
Cytotoxicity refers to all molecules and compounds poisonous to living cells. Thus, cytotoxicity is a broader term than endotoxin. Furthermore, cytotoxic molecules can come from many sources such as manufactured, natural, living, or inanimate sources. On the other hand, endotoxins are LPS sourced from gram-negative bacteria.
What are the differences between bacterial endotoxin testing and cytotoxicity testing?
Bacterial endotoxin testing measures the presence and quantity of endotoxins in a particular sample. In contrast, cytotoxicity is quantified by the biological response of in-vitro cells or in-vivo tissues exposed to a sample. This biological response is evaluated through several means, including cellular degeneration, edema, erythema, and tissue encapsulation. As cytotoxicity and bacterial endotoxin tests measure and identify different toxins, these tests use separate assays to evaluate either cytotoxic poisons or pyrogens, respectively. Cytotoxicity testing follows the method outlined in USP 87 for in-vitro testing and USP 88 for in-vivo testing. In comparison, bacterial endotoxin testing uses the methodologies outlined in USP 85. Note that cytotoxicity testing is not specific enough to confirm that bacterial endotoxins are present or identify the level of bacterial endotoxin contamination of a particular sample.
Why are both bacterial endotoxin testing and cytotoxicity testing important?
Bacterial endotoxin testing is an important quality control step that detects the level of endotoxin contamination of a product at any stage, from initial product manufacture to final distribution. As microorganisms exist on every surface (including our body), bacterial endotoxins can be accidentally introduced during the manufacturing or packaging process in many ways. Some of the most common examples are contamination through the raw materials used, technicians, tubing/piping used to transfer product between development stages in a process, or the manufacturing environment itself. With such abundant sources of contamination, regular endotoxin testing supports the long-term control of manufacturing sites. Bacterial endotoxin testing is essential for medical products or devices that will be inserted into the human body. Suppose bacterial endotoxins exist on the surface of a medical device or product or are present within an injectable product. In that case, the innate immune system of the patient exposed will be activated, causing fever, chills, and potentially death. The example detailed above is why bacterial endotoxic testing is so crucial for medical products and devices.
Cytotoxicity testing evaluates the biological reactivity of mammalian cells and tissues to contact with elastomeric plastics and other polymeric materials that will come in direct or indirect patient contact during medical device or product use. Cytotoxicity is important as it evaluates the biological effects of a sample’s leachable chemicals. The types of cytotoxicity testing to perform for your medical device or product depend upon the final product, the final product’s intended use, and the materials the final product is made of and packaged within. In-vitro methods of cytotoxicity testing include direct contact, agar diffusion, and elution testing. In-vivo methods of cytotoxicity testing include intracutaneous injection, systemic, and implantation testing. Most medical devices and products will only require in-vitro cytotoxicity testing. Reusable devices may require cytotoxicity testing for initial use and device use following recommended reprocessing.
Overall, both bacterial endotoxin and cytotoxicity testing are imperative for the regulatory approval of a medical device or product. These tests ensure that medical devices and products are free of toxins so that patients will not be at risk of pyogenesis, sickness, or organ failure following device exposure or product implantation. Ensure you choose a contract testing organization that can support you with appropriate cytotoxicity and bacterial endotoxin testing for your unique medical device’s or product’s needs.
Ethide Labs is a contract testing organization that specializes in Bacterial Endotoxin Testing. Ethide Labs provides in-vitro cytotoxicity tests in-house and outsources in-vivo cytotoxicity work for toxicity testing of medical devices, products, and drugs. Ethide Labs also offers Sterilization Validations, Bioburden Testing, Microbiology Testing, Environmental Monitoring, EO Residual Testing & Package Integrity Testing services for medical device companies and allied industries. Ethide is an ISO 13485 certified facility.
References
Galanos C. and Freudenberg M. A. Bacterial endotoxins: biological properties and mechanisms of action. Mediators of Inflammation. 1993; 2(7): S11–S16.
