Objective To investigate the role of acyl-coenzyme A: cholesterol acyltransferase inhibitor (ACATI) in apoptosis induced by lipids and whether lipids-induced apoptosis is accompanied by increase of free cholesterol in endoplasmic reticulum (ER)

in order to further understand the mechanism of lipids-induced apoptosis in advanced atherosclerosis. Methods Human vascular smooth muscle cells (VSMCs) and phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 macrophages were used. Tritiated thymidine incorporation was applied to detect cell proliferation. Cytotoxicity was assessed by lactate dehydrogenase (LDH) release. 4'

6-diamidino-2-phenylindole (DAPI) staining

caspase-3

-7 assay

and Annexin-V/propidium iodide (PI) staining were used to detect apoptosis. High performance liquid chromatography was used in intracellular free cholesterol and cholesterol ester assay. ER free cholesterol was quantified. Results Different lipids had different effects on proliferation and cytotoxicity of VSMCs. 25-hydroxycholesterol (25OHC) had biphasic effects on the proliferation of VSMCs. At low concentration

it stimulated cell proliferation

but turned to proliferation inhibition as concentration reached 15 ug/mL. 25OHC and acetylated low density lipoprotein (AcLDL) could respectively induce apoptosis in human VSMCs and PMA differentiated THP-1 macrophages

which was aggravated by ACATI

accompanied by increase of intracellular free cholesterol content. There was also an increase of cholesterol content in ER with AcLDL-induced apoptosis in THP-1 macrophages. Conclusions Lipids could induce apoptosis

accompanied by increase of intracellular free cholesterol content

which could be augmented by ACATI

suggesting that insults resulting in ER free cholesterol rise might be the initiator of apoptosis.