Abstract 10118: PCSK9 Inhibition Augments the Therapeutic Effect of Ezetimibe in Lowering Intestinal Apolipoprotein B Lipoprotein Production
Ezetimibe is an effective therapy to lower circulating low-density lipoprotein (LDL) cholesterol, a maneuver expected to reduce coronary heart disease (CHD) risk. However, ezetimibe concomitantly raises plasma PCSK9 levels, thus reducing the drug’s full potential for cholesterol lowering. Ezetimibe also reduces plasma triglyceride and apolipoprotein (apo) B levels through mechanisms not entirely clear. The objectives of the current study were to determine: (1) the cellular and molecular mechanisms by which ezetimibe affects the metabolism of triglyceride-rich apoB lipoproteins; and (2) whether the use of siRNAs to knock down PCSK9 would enhance the therapeutic effect of ezetimibe on apoB lipoproteins. Treatment of human enterocytes (optimally polarized CaCo-2 cells) with ezetimibe (50 μM, 24 hours) reduced the cellular expression and secretion of apoB48 by 50% and the expression and secretion of apoB100 by 60-75% (p<0.01 for all vs. untreated cells). PCSK9 knockdown of CaCo-2 cells with siRNA 24 hours prior to ezetimibe treatment significantly reduced cellular apoB levels by a further 30% (P<0.01). Ezetimibe increased enterocyte LDLR protein levels by 200% (p<0.01), PCSK9 siRNA reduced LDLR by 50% (p<0.01), while combination treatment produced an additive effect on LDLR protein reduction (p<0.01). The ezetimibe-induced reduction in enterocyte apoB levels was mediated by: (1) a 60% decrease in apoB mRNA expression (p<0.01 vs. control cells); and (2) enhancement of apoB degradation through both LDLR-dependent and LDLR-independent mechanisms. Ezetimibe-induced enterocyte apoB degradation was associated with a 20% decrease in microsomal triglyceride transfer protein (MTP) activity (p<0.01) and activation of the Akt/Erk insulin signaling pathway. The results of our studies provide evidence that ezetimibe reduces production of apoB-containing triglyceride-rich lipoproteins in human enterocytes. We determined that the effects of ezetimibe on enterocyte apoB are mediated both at the transcriptional level and post-transcriptionally through multiple pathways affecting apoB stabilty. Our studies show that PCSK9 inhibition enhances the effect of ezetimibe on intestinal apoB production.
- © 2013 by American Heart Association, Inc.