Endotoxins, also known as lipopolysaccharides (LPS), are part of the outer membrane of the cell wall of Gram-negative bacteria.
Endotoxin is invariably associated with Gram-negative bacteria, regardless of whether the organisms are pathogenic. Although the term is occasionally used to refer to any cell-associated bacterial toxin, in bacteriology it is properly reserved to refer to this lipopolysaccharide complex. Gram-negative bacteria containing these endotoxins include Escherichia coli, Salmonella, Shigella, Pseudomonas, Neisseria, Haemophilus influenzae, Bordetella pertussis, and Vibrio cholerae (Figure 1).
Figure 1. Endotoxins can influence cell growth, cell differentiation, contractility and protein expression. They trigger the release of tumor necrosis factor (TNF), interleukins-1,6 and 8 and the production of platelet-activating factors, Prostaglandin E and Thromboxane A.1,2
Endotoxins Can Be Measured Using Two Methods
- Measuring a clotting reaction between the endotoxin and a clottable protein in the amoebocytes of Limulus polyphemus, the horseshoe crab
- A much more sensitive photometric test based on a Limulus amoebocyte lysate (LAL) and a synthetic color-producing substrate. The LAL assay is used for the routine check of LPS in biological solutions and was the first detection method to be certified by the FDA. LPS contamination is usually expressed in endotoxin units (EU). Typically, 1 mg LPS corresponds to 1–10 EU.
All endotoxin testing for the Purelink® HiPure Kits was performed by an independent FDA-qualified third party testing facility.
Cytotoxicity measures cell death in the presence of transfection reagents and is dependent on cell type, transfection reagent used, and plasmid DNA purity. Plasmid DNA purified with PureLink® HiPure Plasmid Kits causes very low cytotoxicity (Figure 2).
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