title: Cytotoxic cellular cholesterol is selectively removed by apoA-I via ABCA1.
abstract: Excess intracellular free cholesterol (FC) is cytotoxic. This study examines prevention of FC-induced cytotoxicity in J774 macrophage foam cells by incubation with apolipoprotein AI (apoA-I). J774 were cholesterol enriched using acetylated low-density lipoprotein and FC/phospholipid (PL) dispersions. Treatment with an acyl coenzyme-A:cholesterol acyltransferase (ACAT) inhibitor, in the absence of extracellular acceptors, produced hydrolysis of stored esterified cholesterol (EC) and FC-induced cytotoxicity. Incubation of cells with ACAT inhibitor plus apoA-I resulted in FC efflux (0.39 +/- 0.02%/h) along with a reduction in cytotoxicity (26.30 +/- 5.80%), measured by adenine release. Small unilamellar vesicles (SUV) caused greater FC efflux (0.53 +/- 0.02%/h, P = 0.001), but a modest reduction in cytotoxicity (8.40 +/- 2.70%, P = 0.008). Co-incubation of ACAT inhibitor plus the cholesterol transport inhibitor U18666A or the antioxidant Probucol reduced efflux to apoA-I, but not to SUV. Pre-treatment of J774 foam cells with CTP-cAMP upregulates hormone sensitive lipase (HSL) and further upregulates ATP binding cassette A1 (ABCA1). Using mouse serum as a cholesterol acceptor, CTP-cAMP caused greater protection against FC-induced cytotoxicity compared to cells without pre-treatment, suggesting a role of ABCA1 in removal of cytotoxic FC. We conclude that a cytotoxic pool of FC is located in the plasma membrane, is readily available for efflux to apoA-I, and removal of cytotoxic cholesterol may involve ABCA1.
authors.affiliation: Division of Gasteroenterology and Nutrition, Abramson Research Center, Suite 302, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, 3615 Civic Center Blvd., Philadelphia, PA 19104-8651, USA. weibel@email.chop.edu
authors.forename: Ginny
authors.initials: G
authors.lastname: Kellner-Weibel
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Luke
authors.forename: George H
authors.initials: GH
authors.lastname: Rothblat
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism* / Q000494:pharmacology; D001665:Binding Sites; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D017077:Culture Media, Conditioned; D003570:Cytidine Triphosphate / Q000378:metabolism; D004347:Drug Interactions; D005487:Foam Cells / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010743:Phospholipids / Q000378:metabolism* / Q000494:pharmacology; D011336:Probability; D011341:Probucol / Q000494:pharmacology; D002785:Sterol O-Acyltransferase / Q000032:analysis / Q000378:metabolism*
chemical_list: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D017077:Culture Media, Conditioned; D010743:Phospholipids; D003570:Cytidine Triphosphate; D002784:Cholesterol; D002785:Sterol O-Acyltransferase; D011341:Probucol