9-cis β-Carotene Increased Cholesterol Efflux to HDL in Macrophages

Cholesterol efflux from macrophages is a key process in reverse cholesterol transport and, therefore, might inhibit atherogenesis. 9-cis-beta-carotene (9-cis-beta c) is a precursor for 9-cis-retinoic-acid (9-cis-RA), which regulates macrophage cholesterol efflux. Our objective was to assess whether 9-cis-beta c increases macrophage cholesterol efflux and induces the expression of cholesterol transporters. Enrichment of a mouse diet with beta c from the alga Dunaliella led to beta c accumulation in peritoneal macrophages. 9-cis-beta c increased the mRNA levels of CYP26B1, an enzyme that regulates RA cellular levels, indicating the formation of RA from beta c in RAW264.7 macrophages. Furthermore, 9-cis-beta c, as well as all-trans-beta c, significantly increased cholesterol efflux to high-density lipoprotein (HDL) by 50% in RAW264.7 macrophages. Likewise, food fortification with 9-cis-beta c augmented cholesterol efflux from macrophages ex vivo. 9-cis-beta c increased both the mRNA and protein levels of ABCA1 and apolipoprotein E (APOE) and the mRNA level of ABCG1. Our study shows, for the first time, that 9-cis-beta c from the diet accumulates in peritoneal macrophages and increases cholesterol efflux to HDL. These effects might be ascribed to transcriptional induction of ABCA1, ABCG1, and APOE. These results highlight the beneficial effect of beta c in inhibition of atherosclerosis by improving cholesterol efflux from macrophages.