Organosulfur Garlic-derived Compounds Induce ABCA1 Gene Expression in Raw 264.7 Cells

Abstract

Cardiovascular disease (CVD) is currently the leading cause of death in the United States. One of the key factors in CVD development is cholesterol levels; accumulation of cholesterol in the macrophage has been linked to plaque formation and subsequent heart attack or stroke. ATP-binding cassette transporter A1 (ABCA1) is the protein that facilitates cholesterol efflux out of the macrophage, and increasing this efflux can prevent the macrophage from being a pro-atherogenic foam cell. In addition, garlic-derived organosulfur compounds have been suggested to have cholesterol-lowering effects. The aim of this study was to investigate the effects in mouse macrophages of garlic compounds diallyl disulfide (DADS), allyl mercaptan (AM), and S-allyl-L-cysteine (SAC) on ABCA1 expression compared with trichostatin A (TSA), a drug known to induce ABCA1 via histone modification. RAW 264.7 cells were treated with these compounds for six hours, and RNA was isolated, reverse transcribed, and analyzed for changes in gene expression. ABCA1 expression was induced with DADS, AM, and SAC, but no change was seen in expression of ATP-binding cassette transporter G1 (ABCG1) or HMG Co-A Reductase (HMGCR). Chromatin immunoprecipitation assays showed no significant differences in acetylated histone H3 or H4 in the promoter of ABCA1 due to treatment with DADS. Luciferase reporter assays revealed garlic-induced ABCA1 promoter activation with fragments as short as 75 bp upstream of the transcriptional start site and up to 2500 bp, suggesting the transcriptional upregulation may not be due to histone modification in the promoter. These results show that ABCA1 mRNA is significantly increased by treatment with DADS, SAC, and AM, and this effect may or may not be mediated by histone modification. Additional studies are required to understand the mechanisms underlying this effect.