Metformin ameliorates Ox-LDL-induced foam cell formation in raw264.7 cells by promoting ABCG-1 mediated cholesterol efflux

Aims: The accumulation of lipids in macrophages contributes to the development of atherosclerosis. Cholesterol efflux of lipid-loaded macrophages mediated by ATP binding cassette (ABC) cholesterol transporters, on the other hand, has been shown to attenuate atherosclerosis progression in patients with unknown mechanism. We therefore sought to test the effect of metformin that reduced cardiovascular risk in diabetic patients independent of its hypoglycemia effect on cholesterol transport in murine raw264.7 macrophages. Materials and methods: Mouse raw264.7 macrophages were loaded with Ox-LDL (50 mu g/ml) for 24 h before incubated with metformin (15 mu M) for 24 h. Foam cell formation was assessed by Oil red staining and BIODIPY fluorescent staining as well as cholesterol-ester quantification by commercial kit. Cholesterol uptake and expression of scavenger receptors were detected by flow-cytometry. Cholesterol efflux capacity was measured by fluorescent plate-reader and ABC transporters were detected by Western Blots. Cytokines were detected by ELISA in supernatants and normalized by cellular lysates. Key findings: Our results showed that metformin decreased oxidized low-density lipoprotein (Ox-LDL)-induced cholesterol accumulation and foam cell formation by increasing cholesterol efflux to HDL, which was associated with an upregulation of ABC transporter ABCG-1. Moreover, metformin increased Ox-LDL-impaired IL-10 secretion, an important anti-foam cell cytokine in atherosclerosis. Significance: Our data highlighted the therapeutic potential of targeting macrophage cholesterol efflux with new or existing drugs for the possible reduction of foam cell formation in the prevention and treatment of diabetesaccelerated atherosclerosis.