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ARS Home » Southeast Area » Little Rock, Arkansas » Microbiome and Metabolism Research Unit » Research » Publications at this Location » Publication #349144
Title: Is palmitate truly pro-inflammatory? Experimental confounders and context-specificity

Author
item ONO-MOORE, KIKUMI - Arkansas Children'S Nutrition Research Center (ACNC)
item BLACKBURN, MICHAEL - University Arkansas For Medical Sciences (UAMS)
item Ferruzzi, Mario

Submitted to: American Journal of Physiology - Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2018
Publication Date: 7/17/2018
Citation: Ono-Moore, K.D., Blackburn, M.L., Adams, S.H. 2018. Is palmitate truly pro-inflammatory? Experimental confounders and context-specificity. American Journal of Physiology - Endocrinology and Metabolism. http://doi.org/10.1152/ajpendo.00187.2018.
DOI: https://doi.org/10.1152/ajpendo.00187.2018

Interpretive Summary: Based primarily on cell culture experiments, saturated fatty acids (SFAs) are thought to promote inflammation (TNF-a and IL-6) and contribute to metabolic diseases (diabetes) through toll-like receptor activation. Studies are often complicated by a requirement for carriers (e.g. bovine serum albumin, BSA) or solvents (e.g. ethanol) to increase SFA solubility: BSA can induce inflammation and ethanol is known to kill cells. To determine if these factors influence SFA-associated inflammation, we measured responses of RAW264.7 macrophages (immune cells) and C2C12 myotubes (muscle cells) to various BSA and ethanol conditions. BSA preparations activated, whereas 0.5-1.0% ethanol inhibited, RAW264.7 TNF-a release; ethanol modestly increased IL-6 secretion in C2C12 myotubes. Using a lower-inflammation BSA source and no ethanol, ~24 hr sodium palmitate (a saturated fat) treatment (up to 600 uM) failed to trigger RAW264.7 TNF-a release, and significantly dampened BSA-induced inflammation. In C2C12 myotubes, only high palmitate concentrations elicited IL-6 secretion, and acute palmitate treatments did not activate MAP-kinase pathways above that of fresh media alone. These results highlight the importance of experimental conditions in studies exploring SFA inflammation effects. The limited (or even anti-inflammatory) effects of palmitate that we observed indicate the effects of SFAs have on the immune system are context-specific. Thus, caution is needed when interpreting the literature related to supposed pro-inflammatory effects of SFA.

Technical Abstract: Based primarily on cell culture results, saturated fatty acids (SFAs) are proposed to promote inflammation and contribute to metabolic dysfunction through toll-like receptor activation. Studies are often complicated by a requirement for carriers (e.g. BSA) or solvents (e.g. ethanol) to increase SFA solubility: BSA can itself induce inflammation and ethanol is a cytotoxin. To ascertain if these factors influence interpretations of SFA-associated inflammation activity, we measured responses of RAW264.7 monocyte/macrophages and C2C12 myotubes to various BSA, ethanol and cyclodextrin (alternative FA carrier) conditions. Fatty acid free low-endotoxin BSA preparations (0.33% to 2% wt/vol) activated, whereas 0.5-1.0% ethanol inhibited, RAW264.7 TNF-alpha release. Ethanol modestly increased IL-6 secretion in C2C12 myotubes. Cyclodextrins (0.3 – 6.0 mM) were tested as alternative carrier of palmitate, their usefulness in cell culture was limited due to toxicity and solubility issues. Using a lower-inflammation BSA source and no ethanol, ~24 hr sodium palmitate treatment (up to 600 µM) failed to trigger RAW264.7 TNF-alpha release, and in fact significantly dampened BSA-induced inflammation by >50%. In C2C12 myotubes, only high palmitate concentrations (500-600 uM) elicited IL-6 secretion (> 2.5-fold increase). Acute palmitate (200 or 500 uM) treatment did not activate MAP-kinase pathways above that of fresh media alone in either cell type. These results highlight the importance of experimental conditions in studies exploring SFA inflammation effects. The limited (or even anti-inflammatory) effects of palmitate that we observed indicate that immunomodulatory effects of SFAs are context-specific. Thus, caution is needed when interpreting the literature related to putative pro-inflammatory effects of SFA.