Differences in hypolipidaemic effects of two statins on Hep G2 cells or human hepatocytes in primary culture

Intracellular cholesterol-binding proteins enhance HDL-mediated cholesterol uptake in cultured primary mouse hepatocytes

A major gap in our knowledge of rapid hepatic HDL cholesterol clearance is the role of key intracellular factors that influence this process. Although the reverse cholesterol transport pathway targets HDL to the liver for net elimination of free cholesterol from the body, molecular details governing cholesterol uptake into hepatocytes are not completely understood. Therefore, the effects of sterol carrier protein (SCP)-2 and liver fatty acid-binding protein (L-FABP), high-affinity cholesterol-binding proteins present in hepatocyte cytosol, on HDL-mediated free cholesterol uptake were examined using gene-targeted mouse models, cultured primary hepatocytes, and 22-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-amino]-23,24-bisnor-5-cholen-3β-ol (NBD-cholesterol). While SCP-2 overexpression enhanced NBD-cholesterol uptake, counterintuitively, SCP-2/SCP-x gene ablation also 1) enhanced the rapid molecular phase of free sterol uptake detectable in <1 min and initial rate and maximal uptake of HDL free cholesterol and 2) differentially enhanced free cholesterol uptake mediated by the HDL3, rather than the HDL2, subfraction. The increased HDL free cholesterol uptake was not due to increased expression or distribution of the HDL receptor [scavenger receptor B1 (SRB1)], proteins regulating SRB1 [postsynaptic density protein (PSD-95)/Drosophila disk large tumor suppressor (dlg)/tight junction protein (ZO1) and 17-kDa membrane-associated protein], or other intracellular cholesterol trafficking proteins (steroidogenic acute response protein D, Niemann Pick C, and oxysterol-binding protein-related proteins). However, expression of L-FABP, the single most prevalent hepatic cytosolic protein that binds cholesterol, was upregulated twofold in SCP-2/SCP-x null hepatocytes. Double-immunogold electron microscopy detected L-FABP sufficiently close to SRB1 for direct interaction, similar to SCP-2. These data suggest a role for L-FABP in HDL cholesterol uptake, a finding confirmed with SCP-2/SCP-x/L-FABP null mice and hepatocytes. Taken together, these results suggest that L-FABP, particularly in the absence of SCP-2, plays a significant role in HDL-mediated cholesterol uptake in cultured primary hepatocytes.

The double-faced metabolic and inflammatory effects of standard drug therapy in patients after percutaneous treatment with drug-eluting stent

OBJECTIVE

The inflammatory responses after percutaneous coronary intervention (PCI) with drug-eluting stent (DES) remain poorly understood; therefore, this study aims to investigate the changes of metabolic parameters and systematic inflammatory status of circulating mononuclear cells (MNC) in patients after percutaneous treatment with DES implantation.

METHODS AND RESULTS

Twenty-seven patients with acute coronary syndrome who would undergo PCI with DES implantation were consecutively recruited and treated with standard drug therapy from the start of hospitalization. Metabolic parameters including total cholesterol, triglycerides, high-density lipoprotein, low-density lipoprotein improved significantly after 12 weeks of standard medication, whereas the plasma levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), macrophage migration inhibitory factor (MIF), and matrix metalloproteinase-9 (MMP-9) increased (P=0.012, 0.035, 0.062 and 0.112, respectively, compared to the baseline). The NF-κB DNA binding activity in MNC increased significantly compared to the baseline (P=0.015), whereas IκB-β and PPAR-γ were significantly suppressed (P=0.046 and 0.002, respectively). There were strong correlations among the changes of metabolic parameters and the changes of proinflammatory factors; however, none of them is statistically significant.

CONCLUSIONS

Standard drug therapy can improve the metabolic parameters but fail to restrain the proinflammatory state after PCI with DES implantation. Longer term endpoint-based studies are still needed for further exploration of the relationship between inflammatory factors and clinical cardiovascular events in the era of DES.

Dysregulation of the mevalonate pathway promotes transformation

The importance of cancer metabolism has been appreciated for many years, but the intricacies of how metabolic pathways interconnect with oncogenic signaling are not fully understood. With a clear understanding of how metabolism contributes to tumorigenesis, we will be better able to integrate the targeting of these fundamental biochemical pathways into patient care. The mevalonate (MVA) pathway, paced by its rate-limiting enzyme, hydroxymethylglutaryl coenzyme A reductase (HMGCR), is required for the generation of several fundamental end-products including cholesterol and isoprenoids. Despite years of extensive research from the perspective of cardiovascular disease, the contribution of a dysregulated MVA pathway to human cancer remains largely unexplored. We address this issue directly by showing that dysregulation of the MVA pathway, achieved by ectopic expression of either full-length HMGCR or its novel splice variant, promotes transformation. Ectopic HMGCR accentuates growth of transformed and nontransformed cells under anchorage-independent conditions or as xenografts in immunocompromised mice and, importantly, cooperates with RAS to drive the transformation of primary mouse embryonic fibroblasts cells. We further explore whether the MVA pathway may play a role in the etiology of human cancers and show that high mRNA levels of HMGCR and additional MVA pathway genes correlate with poor prognosis in a meta-analysis of six microarray datasets of primary breast cancer. Taken together, our results suggest that HMGCR is a candidate metabolic oncogene and provide a molecular rationale for further exploring the statin family of HMGCR inhibitors as anticancer agents.

In vitro assay for drug-induced hepatosteatosis using rat primary hepatocytes, a fluorescent lipid analog and gene expression analysis

To evaluate new drugs' potential for hepatosteatosis, we developed a cell-based assay using a fluorescent fatty acid analog: BODIPY558/568 C12. Rat primary hepatocytes were exposed to positive reference compounds [cyclosporine A (CsA), clofibrate (CFR), tetracycline (TC), valproic acid (VPA), carbon tetrachloride (CCl4), tamoxifen (TMX)] in the presence of BODIPY558/568 C12. The formation of fluorscecent particles or lipid droplets in the cytoplasm was confirmed by confocal laser scanning microscopy and electron microscopy respectively. The accumulation of BODIPY558/568 C12 was measured by fluorometry and high content imaging method. All positive reference compounds increased fluorescent particles in number and fluorescence intensity. High content imaging was more sensitive and selective method than fluorometry to detect fluorescent particles. Gene expression analysis of the hepatocytes showed two patterns: genes related to lipid metabolism/synthesis were down-regulated by oxidative stress inducing compounds: CsA, TC and TMX, and up-regulated by peroxisome proliferator-activated receptor-alpha agonists: CFR and VPA. From these findings, we concluded that the cell-based assay developed in this study is an appropriate method to predict drugs' potential for hepatosteatosis, and gene expression analysis is useful to profile the mechanism of the hepatosteatosis.

Statins and transcriptional regulation: The FXR connection

Farnesoid X receptor (FXR) is a nuclear receptor involved in lipoprotein as well as glucose metabolism. Statins are widely used hypolipidemic agents with many pleiotropic actions. It is known that statins affect other nuclear hormone receptors, but no reports are available on the effect of these drugs on FXR. Employing an animal model (Syrian hamsters), we hereby present evidence to demonstrate that Simvastatin, a broadly prescribed statin, decreases the expression of FXR at both the RNA and protein levels and down-regulates its DNA-binding activity. This novel property may have important implications on the mode statins influence on lipoprotein and carbohydrate homeostasis in the organism.

Pitavastatin, a Potent Hydroxymethylglutaryl Coenzyme a Reductase Inhibitor, Increases Cholesterol 7 .ALPHA.-Hydroxylase Gene Expression in HepG2 Cells

BACKGROUND

The effect of pitavastatin on the mRNA levels of apolipoprotein (apo) A-I, peroxisome proliferator-activated receptor alpha (PPARalpha), cholesterol 7alpha-hydroxylase (CYP7A1), and farnesoid X receptor (FXR) in HepG2 cells was examined to establish whether pitavastatin affects bile acid synthesis and if so, to determine a possible molecular mechanism.

METHODS AND RESULTS

HepG2 cells were cultured in serum-free Dulbecco's modified Eagle medium for 18 h before drug treatment. Total RNA was extracted at set times and mRNA levels were quantified by reverse transcription-real time polymerase chain reaction. Pitavastatin at 0.1, 1, 5, and 10 micromol/L increased the mRNA levels of apo A-I, PPARalpha, CYP7A1, and FXR in a dose-dependent manner. The mRNA levels of apo A-I, PPAR alpha, CYP7A1, and FXR similarly increased with increasing doses of pitavastatin. Coincubation of mevalonate (4 mmol/L) with pitavastatin (5 micromol/L) reversed the inductive effects of pitavastatin on the mRNA levels of these genes, indicating that the inductive effects of pitavastatin were related to its inhibition of HMG-CoA reductase.

CONCLUSIONS

Pitavastatin increased the mRNA levels of CYP7A1 in HepG2 cells, suggesting that increased conversion of cholesterol to bile acids may be the mechanism for its potent low-density lipoprotein cholesterol-lowering effects.