Destruction of Typical Endotoxins by Dry Heat as Determined Using LAL Assay and Pyrogen Assay

Abstract

The kinetics of destruction by dry heat of two typical endotoxins, Escherichia coli 055:B5 (E. coli endotoxin) and Salmonella abortus equi (S. abortus equi endotoxin), were determined using the Limulus Amebocyte Lysate (LAL) and pyrogen assays. The efficiency of recovery of these endotoxins from carriers using a pyrogen assay was also determined simultaneously. In the LAL assay 0.1–10,000 EU was used and 10–1000 EU in the pyrogen assay. Recoveries of E. coli endotoxin and S. abortus equi endotoxin were, respectively, 49.7–92.0% and 27.0–70.1% by the LAL assay, and 31.1% and 60.6% by the pyrogen assay. Fourier transformation infrared (FT–IR) spectra demonstrated the presence of chemical structural differences between the two endotoxins. By dry heat (200 or 250°C), there were no significant differences in the destruction kinetics between the two endotoxins; either endotoxin can therefore be adapted for use in the endotoxin challenge test. Destruction in the pyrogen assay was significantly quicker than that predicted by the LAL assay for each of the two endotoxins. In this endotoxin destruction system, 3 log cycle reduction (the United State Pharmacopeia (USP) recommendation for the depyrogenation process) could not be obtained by challenge with 10,000 EU of endotoxin under the depyrogenation conditions of 200°C for 60 min (a set of conditions described in the European Pharmacopoeia (EP)), though little pyrogenicity remained. On the other hand, at 250°C for 30 min (a set of conditions described in the EP, USP and Pharmacopoeia of Japan (JP)), a 3 log cycle reduction was achieved without any pyrogenicity remaining.