Pitavastatin effect on ATP binding cassette A1-mediated lipid efflux from macrophages: evidence for liver X receptor (LXR)-dependent and LXR-independent mechanisms of activation by cAMP

J Pharmacol Exp Ther. 2006 Apr;317(1):395-401. doi: 10.1124/jpet.105.093930. Epub 2006 Jan 13.

Abstract

The promotion of lipid efflux from macrophages is an important ATP binding cassette A1 (ABCA1)-mediated antiatherosclerotic mechanism that prevents peripheral tissues from foam cell accumulation. Statins exert beneficial antiatherosclerotic effects on cardiovascular disease correlated to the cholesterol-lowering properties and the pleiotropic activities. In this work, we investigated the ability of statins to modulate ABCA1-mediated lipid efflux from macrophages, where the protein expression was differently induced. Pitavastatin (0.1-10 microM) and compactin (10 microM) reduced both cholesterol and phospholipid efflux up to 60% from macrophages expressing ABCA1 upon treatment with 8-(4-chlorophenylthio)-cyclic AMP (cpt-cAMP), and this was secondary to a reduction of ABCA1 mRNA and protein content. Conversely, statins did not affect ABCA1 activity when the protein was up-regulated by 22-hydroxycholesterol/9-cis-retinoic acid or through cholesterol loading. Statin inhibition of lipid efflux induced by cpt-cAMP was reversed in the presence of mevalonate, 22-hydroxycholesterol, and cholesterol but not geranyl geraniol. In macrophages obtained from liver X receptor (LXR)-deficient mice, cpt-cAMP still promoted cholesterol efflux, but pitavastatin did not exert any effect. The present work shows that statins may inhibit ABCA1-mediated lipid efflux in macrophages only when ABCA1 protein expression is induced by cpt-cAMP and provides evidence that cAMP may activate ABCA1 independently of an increase of intracellular sterol synthesis but through at least two pathways: one independent of LXR and one involving an intracellular sterol(s) acting as LXR ligand(s). In addition, the lack of inhibitory effect on lipid efflux in cholesterol-loaded macrophages is likely to exclude a potential negative pleiotropic effect by statins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter 1
  • ATP-Binding Cassette Transporters / biosynthesis*
  • Animals
  • Blotting, Western
  • Cells, Cultured
  • Cholesterol / metabolism
  • Cyclic AMP / physiology*
  • DNA-Binding Proteins / physiology*
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors / pharmacology*
  • Lipid Metabolism / drug effects*
  • Liver X Receptors
  • Macrophages, Peritoneal / drug effects*
  • Macrophages, Peritoneal / metabolism
  • Mice
  • Orphan Nuclear Receptors
  • Phospholipids / metabolism
  • Quinolines / pharmacology*
  • Receptors, Cytoplasmic and Nuclear / physiology*
  • Reverse Transcriptase Polymerase Chain Reaction

Substances

  • ATP Binding Cassette Transporter 1
  • ATP-Binding Cassette Transporters
  • DNA-Binding Proteins
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors
  • Liver X Receptors
  • Orphan Nuclear Receptors
  • Phospholipids
  • Quinolines
  • Receptors, Cytoplasmic and Nuclear
  • Cholesterol
  • Cyclic AMP
  • pitavastatin