Docosahexaenoic Acid Decreases Pro-Inflammatory Mediators in an <i>In Vitro</i> Murine Adipocyte Macrophage Co-Culture Model

<div><p>Paracrine interactions between adipocytes and macrophages contribute to chronic inflammation in obese adipose tissue. Dietary strategies to mitigate such inflammation include long-chain polyunsaturated fatty acids, docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, which act through PPARγ-dependent and independent pathways. We utilized an <i>in vitro</i> co-culture model designed to mimic the ratio of macrophages:adipocytes in obese adipose tissue, whereby murine 3T3-L1 adipocytes were cultured with RAW 264.7 macrophages in direct contact, or separated by a trans-well membrane (contact-independent mechanism), with 125 µM of albumin-complexed DHA, EPA, palmitic acid (PA), or albumin alone (control). Thus, we studied the effect of physical cell contact versus the presence of soluble factors, with or without a PPARγ antagonist (T0070907) in order to elucidate putative mechanisms. After 12 hr, DHA was the most anti-inflammatory, decreasing MCP1 and IL-6 secretion in the contact system (−57%, −63%, respectively, p≤0.05) with similar effects in the trans-well system. The trans-well system allowed for isolation of cell types for inflammatory mediator analysis. DHA decreased mRNA expression (p<0.05) of <i>Mcp1</i> (−7.1 fold) and increased expression of the negative regulator, <i>Mcp1-IP</i> (+1.5 fold). In macrophages, DHA decreased mRNA expression of pro-inflammatory M1 polarization markers (p≤0.05), <i>Nos2</i> (iNOS; −7 fold), <i>Tnfα</i> (−4.2 fold) and <i>Nfκb</i> (−2.3 fold), while increasing anti-inflammatory <i>Tgfβ1</i> (+1.7 fold). Interestingly, the PPARγ antagonist co-administered with DHA or EPA in co-culture reduced (p≤0.05) adiponectin cellular protein, without modulating other cytokines (protein or mRNA). Overall, our findings suggest that DHA may lessen the degree of MCP1 and IL-6 secreted from adipocytes, and may reduce the degree of M1 polarization of macrophages recruited to adipose tissue, thereby decreasing the intensity of pro-inflammatory cross-talk between adipocytes and macrophages in obese adipose tissue.</p>