Effect of different sample treatment methods on Low Endotoxin Recovery Phenomenon

Endotoxin is a kind of lipopolysaccharide that exits on the cell wall of Gram-negative bacteria. It can cause fever, shock or even death when is delivered into human body. So, it is necessary to control the endotoxin contamination for biopharmaceutical products that are mainly administered by intravenous route. Limulus Amebocyte Lysate (LAL)-based tests are usually used to detect endotoxin content in biologics formulations. However, an undesirable phenomenon called "Low Endotoxin Recovery (LER)" often occurs in formulation buffers that usually contain chelating component, such as sodium citrate, and amphiphilic surfactant, such as Tween-20. The occurrence of this LER phenomenon may interfere with endotoxin detection and cause false negative results. In this study, we compared the effect of different sample treatment methods on endotoxin detection and found that the LER phenomenon was better controlled under the conditions of low pH (pH = 5.0), low temperature (2-8 °C) and in the presence of divalent cations in the solution. In addition, although the endotoxin activity was found to have decreased due to LER phenomenon, the particle size distribution of endotoxin determined by dynamic light scattering (DLS) in LER solution did not change obviously, which is different from previous hypothesis about LER phenomenon in literature that the particle size of endotoxin aggregates would decrease under LER conditions. These findings provide some insights into different sample treatment methods for endotoxin detection and give a better understanding and solution on minimizing the LER phenomenon.