Is palmitate truly proinflammatory? Experimental confounders and context-specificity

• Published in: American journal of physiology: endocrinology and metabolism 2018-11, Vol.315 (5), p.E780-E794
• Main Authors: Ono-Moore, Kikumi D, Blackburn, Michael L, Adams, Sean H
• Format: Article
• Language: English
• Subjects: Animals; Cell culture; Cell Death - drug effects; Cell Death - physiology; Cell Differentiation - drug effects; Cell Differentiation - physiology; Cell Line; Cyclodextrin; Cyclodextrins; Ethanol; Ethanol - pharmacology; Fatty acids; Immunomodulation; Inflammation; Inflammation - metabolism; Interleukin 6; Interleukin-6 - metabolism; Kinases; Macrophages; Macrophages - metabolism; MAP kinase; Mice; Monocytes; Myoblasts - metabolism; Myotubes; Palmitic acid; Palmitic Acid - pharmacology; Phosphorylation - drug effects; Receptor mechanisms; Signal Transduction - drug effects; Signal Transduction - physiology; Sodium; Solubility; Toll-like receptors; Toxicity; Tumor necrosis factor-α
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.00187.2018

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. To ascertain whether these factors influence interpretations of SFA-associated inflammation activity, we measured responses of RAW264.7 monocyte/macrophages and C C 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 TNFα release. Ethanol modestly increased IL-6 secretion in C C myotubes. Cyclodextrins (0.3-6.0 mM) were tested as alternative carriers of palmitate, but their usefulness was limited due to toxicity and solubility issues. Using a lower-inflammation BSA source and no ethanol, ∼24-h sodium palmitate treatment (≤600 µM) failed to trigger RAW264.7 TNFα release and, in fact, significantly dampened BSA-induced inflammation by >50%. In C C myotubes, only high palmitate concentrations (500-600 µM) elicited IL-6 secretion (>2.5-fold increase). Acute palmitate (200 or 500 µM) treatment did not activate MAP kinase pathways above that of fresh BSA-containing 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 proinflammatory effects of SFA.