Low Endotoxin Recovery (LER) is the observation that, for many biological compounds, it is difficult to recover known endotoxin spikes. This has become the prevailing topic in the endotoxin field since the inability of LAL to detect endotoxin does not necessarily preclude a pyrogenic reaction in vivo. A recent publication by scientists at Eli Lilly highlight the technical problems involved with measuring LER and insights into its cause.
First, while the cause of LER has not been directly demonstrated, it is thought to be a function of the aggregation state of endotoxin monomers. Evidence of this is the observation that divalent cations and surfactants, which destabilize endotoxin aggregates, are usually involved in LER. This report shows that while cations and surfactants are essential in LER, they are not sufficient. Second, the paper shows the importance of a stringent testing protocol. The use of the verified USP <85> method for routine batch release testing resulted in acceptable endotoxin recovery (50-200%). However, changing small details such as mixing time and sampling scheme produced inconsistent results. Finally, they provide evidence that naturally occurring endotoxin (NOE) is not as susceptible to LER as a purified stock, indicating the importance of the supramolecular structure.
BioDtech has previously observed similar masking issues as a result of interactions between protein molecules and endotoxin. In response, we have developed the EndoPrep system to remove interfering proteins from samples and allow complete endotoxin recovery.