Exacerbation of toxic effects by endotoxin contamination of recombinant human tumor necrosis factor

The toxic effects of endotoxin-free human recombinant tumor necrosis factor (rH-TNF), shown to contain less than 50 pg endotoxin/mg rH-TNF, were investigated and compared with those of rH-TNF and endotoxin coadministered at 4-400 ng endotoxin/mg rH-TNF in female Sprague-Dawley rats. The mean lethal dose of 5.9 mg/kg rH-TNF found for the endotoxin-free rH-TNF was far higher than that attributed to rH-TNF by other investigators. Coadministration with endotoxin derived from E. Coli. Salmonella abortus equi, or Serratia marcescens reduced the apparent mean lethal dose of rH-TNF in correspondence to the endotoxin concentration, with a value of 0.7 mg/kg rH-TNF observed at 1600 ng, 757 ng, and 5260 ng endotoxin/mg rH-TNF, respectively. Coadministration also resulted in more severe histopathologic and physicochemical effects than rH-TNF alone. Histopathologic abnormalities observed only in coadministration included interlobular edema and hemorrhage of the pancreas and, most remarkably, splenomegaly, which was not observed with rH-TNF alone even at lethal doses. The results indicate that particular care in determining endotoxin contamination is essential in any consideration of TNF toxicity.