The Effects And Mechanisms Of Il-18 On The Down-regulation Of ABCA1 In Foam Cells

Objective: IL-18 and IL-12, mainly produced by activated macrophages, are multifunctional cytokines which have been found to be excessively expressed in inflammatory atherosclerosis lesions.This study was to investigate the changes of cholesterol efflux, ATP-binding cassette transporter A1 (ABCA1) mRNA and protein expression in THP-1 macrophage derived foam cells after treated by IL-18, IL-12, or both, and to discover the combined effects and mechanisms of IL-18 and IL-12 on the down-regulation of ABCA1 in foam cells.Methods: We first induced THP-1 cells to become macrophages by phorbol. Then THP-1 macrophages were induced to be foam cells by ox-LDL. The foam cells were exposed to IL-18 with different levels(0,2,20,200 ng/ml)or IL-12 with different level(s0,0.2,2,20 ng/ml)for 24 hours or exposed to 20ng/ml IL-18 and 2ng/ml IL-12 for increasing periods of time(0,3,6,12,24h). Our experiment also used 20ng/ml IL-18 and 2ng/ml IL-12 or together with 50ng/μL IL-18BP or 20μM N-p-Tosyl-L-phenylalanine chloromethyl ketone (TPCK) to pretreat (3 hours) THP-1 macrophage derived foam cells for 24 hours. Cellular lipid accumulation was determined by high performance liquid chromatography analysis. Cholesterol efflux was determined by FJ-2107P type liquid scintillator. IL-18R, ABCA1 and LXRαmRNA were measured by real-time quantitative PCR(RT-PCR). Western blotting was used to determine protein levels for IL-18R, ABCA1, LXRαand intranuclear NF-κB p65.Results: Our experiments show that the lipid accumulation and the cellular cholesterol efflux in THP-1 macrophage derived foam cells were only weakly influenced by IL-18 or IL-12, but were significantly influenced by combined treatment with IL-18 and IL-12. Combined treatment with IL-18 and IL-12 can decrease the expression of ABCA1 mRNA and protein levels in dose-and time-dependent manner, but increase intranuclear NF-κB p65 protein levels. The LXRαmRNA and protein expression were not affected by IL-18 and/or IL-12. Pretreatment with IL-18BP and TPCK, a NF-κB inhibitor, can partly reverse the effect of IL-18 and IL-12. IL-12 is prerequisite to exert the action of IL-18 via up-regulating the expression of IL-18R.Conclusions: These findings suggest that combined treatment with IL-18 and IL-12 can down-regulate the expression of ABCA1 mRNA and protein, promote the accumulation of lipid and decrease cellular cholesterol efflux in THP-1 macrophage derived foam cells. The mechanism may have relationship with IL-18R-NF-κB pathway in LXRα-independent manner.