Journal
TRANSPLANTATION
Volume 84, Issue 8, Pages 1029-1036Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1097/01.tp.0000286095.55685.e9
Keywords
Hyperlipidemia; inflammatory stress; human hepatocytes.
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Background. Sirolimus is a potent immunosuppressive agent, which is associated with dyslipidemia in clinical transplantation. The present study was undertaken to investigate the potential hepatocyte mechanisms by which sirolimus causes dyslipidemia. Methods. Using both a quantitative assay of intracellular cholesterol and an [(3)H] -labeled cholesterol efflux assay, we studied the effect of sirolimus on cholesterol accumulation and cholesterol efflux in HepG2 cells in the absence or presence of inflammatory stress induced by interleukin-1 beta. The gene and protein expression of molecules involved in cholesterol homeostasis were examined by real-time reverse-transcription polymerase chain reaction and Western blotting. Results. Sirolimus inhibited low-density lipoprotein (LDL) receptor (LDLr)-mediated cholesterol ester accumulation induced by interleukin-1 beta in HepG2 cells. This inhibitory effect was mediated by down-regulation of sterol regulatory element-binding proteins (SREBP) cleavage activating protein (SCAP) and SREBP-2 mRNA expression. Using confocal microscopy, we demonstrated that sirolimus reduced translocation of SCAP-SREBP2 complex from endoplasmic reticulum to Golgi for activation, thereby inhibiting LDLr gene transcription. Reduction of LDLr in the liver may result in a delay of LDL-cholesterol clearance from circulation causing an increase of plasma cholesterol concentration. Furthermore, sirolimus increased cholesterol efflux mediated by adenosine triphosphate- binding cassette transporter A1 gene expression by increasing peroxisome proliferator-activated receptor-alpha and liver X receptor-alpha gene and protein expression. Increased cholesterol efflux from HepG2 cells may increase high-density lipoprotein cholesterol level and also contribute to apolipoprotein B lipoprotein formation by enhancing transfer of high-density lipoprotein cholesterol to apolipoprotein B lipoproteins. Conclusions. This study demonstrates that the increase of LDL cholesterol by sirolimus is partly due to the reduction of LDLr on hepatocytes.
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