Pro-inflammatory effects of commercial alpha-lactalbumin on RAW 264.7 macrophages is due to endotoxin contamination

This study investigated the effects of alpha-lactalbumin (alpha-LA) on cellular signaling molecules associated with inflammatory responses in RAW 264.7 macrophages. The results indicated that commercial alpha-LA could increase prostaglandin E-2 (PGE(2)) and the expression of COX-2 via increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38 mitogen-activated protein kinase (MAPK) and jun N-terminal kinase (JNK), and increase nitric oxide (NO) and the expression of iNOS via the activation of ERK1/2 and JNK. Furthermore, commercial alpha-LA could increase nuclear translocation of p65 nuclear factor-kappa B (p65 NF-kappa B) through stimulation on inhibitor kappa 8-alpha (1 kappa B-alpha) degradation. Since endotoxin also has these effects, we assayed the content of endotoxin in the commercial alpha-LA. We found to our surprise that endotoxin was there and that alpha-LA-induced NO and PGE(2) production could be suppressed by polymyxin B, a specific inhibitor of endotoxin. Thus, the pro-inflammatory effects of commercial alpha-LA might be caused by endotoxin contamination through activation and expression of iNOS and COX-2 which were upregulated by MAPKs or nuclear translocation of p65 NF-kappa B in RAW 264.7 cells. It is therefore crucial to assess the possibility of endotoxin contamination within any biological product being studied for immune augmenting activities before a meaning result can be obtained. (C) 2010 Elsevier Ltd. All rights reserved.