Conjugated linoleic acid induces an atheroprotective macrophage MΦ2 phenotype and limits foam cell formation

BACKGROUND: Atherosclerosis, the underlying cause of heart attack and strokes, is a progresive dyslipidemic and inflammatory disease where monocyte-derived macrophage cells play a pivotal role. Although most of the mechanisms that contribute to the progression of atherosclerosis have been identified, there is limited information on those governing regression. Conjugated linoleic acid (CLA) is a group of isomers of linoleic acid that differ in the position and/or geometry of their double bonds. We have previously shown that a specific CLA blend (80:20 cis-9,trans-11:trans-10,cis-12-CLA) induces regression of pre-established atherosclerosis in vivo, via modulation of monocyte/macrophage function. However, the exact mechanisms through which CLA mediates this effect remain to be elucidated. METHODS: Here, we address if CLA primes monocytes towards an anti-inflammatory MΦ2 macrophage and examine the effect of individual CLA isomers and the atheroprotective blend on monocyte-macrophage differentiation, cytokine generation, foam cell formation and cholesterol metabolism in human peripheral blood monocyte (HPBMC)-derived macrophages. RESULTS: cis-9,trans-11-CLA and the atheroprotective 80:20 CLA blend regulates expression of pro-inflammatory mediators and modulates the inflammatory cytokine profile of macrophages and foam cells. In addition, cis-9,trans-11-CLA and CLA blend primes HPBMCs towards an anti-inflammatory MΦ2 phenotype, characterised by increased scavenger receptor (CD36) and efflux protein (ABCA-1) expression. Furthermore, this altered macrophage phenotype impacts on foam cell formation, inhibiting ox-LDL accumulation and promoting cholesterol efflux via both PPARγ and LXRα dependent pathways. CONCLUSION: The data increases the understanding of the pathways regulated by CLA in atheroprotection, namely, inhibiting the progressive acquisition of a pro-inflammatory macrophage phenotype.