Saturated fatty acid (SFA)‐induced activation of proinflammatory pathways is fatty acid‐specific effects not due to the contaminants in BSA

Toll‐like receptor 4 (TLR4) and TLR2 can be activated by SFAs but inhibited by docosahexaenoic acid (DHA). TLR deletion/mutant mice are protected from saturated fat diet‐induced inflammatory responses and insulin resistance. However, one report (ATVB 11:1944, 2009) suggested that SFA‐induced TLR activation is due to contaminants in BSA used for conjugation of fatty acids. This report casted doubt about proinflammatory effects of SFAs. Here, we present multiple evidence for proinflammatory effects of SFAs. Sodium laurate (in RAW264.7 macrophage) or palmitate (in THP‐1 monocyte) without BSA induced TLR target gene expression when cultured in low FBS (0.25%) media. However, unconjugated DHA inhibited SFA‐induced TLR target gene expression in both RAW264.7 and THP‐1 cells. Since BSA was not used in these experiments, contaminants in BSA have no relevance in interpreting the results. LPS‐induced, but not SFA‐induced, TLR4 target gene expression was abolished by polymixin B. Unlike suspension cells (THP‐1), BSA conjugation is required for palmitic acid (PA) to induce TLR target gene expression in adherent cell (RAW264.7). BSA (Fitzgerald # 30‐AB79) alone at concentrations used for conjugation of PA did not induce TLR target gene expression. Together, these results indicate that SFA‐induced TLR target gene expression is a fatty acid‐specific effect, not due to contaminants in BSA (NIH DK064007:DK078328‐02S1).