Adsorption of endotoxins on glass in the presence of cationic proteins

Endotoxin activity was detected in empty glass tubes where endotoxins were incubated with lysozyme, histone or RNaseA, indicating adsorption of endotoxins on glass in the presence of cationic proteins. In the case of lysozyme, the recovery of spiked endotoxins (90.0%) using polystyrene tubes for incubation was much greater than the recovery (28.5%) using glass tubes, suggesting that lysozyme-mediated adsorption of endotoxins on glass is a major cause of poor recovery of spiked endotoxins in the LAL assay using glass tubes. In contrast, the recovery of spiked endotoxins (64.7%) using polystyrene tubes in the presence of the non-cationic protein BSA was less than the recovery (103.9%) using glass tubes. The difference in endotoxin recovery using glass or polystyrene tubes in the presence of cationic proteins or BSA can be explained by differences in protein adsorption on the tubes. Consequently, care must be exercised in selecting containers used for the LAL assay of proteins which bind to endotoxins.