Pitavastatin Increases ABCA1 Expression by Dual Mechanisms: SREBP2-Driven Transcriptional Activation and PPARα-Dependent Protein Stabilization but Without Activating LXR in Rat Hepatoma McARH7777 Cells

Potential Therapeutic Agents That Target ATP Binding Cassette A1 (ABCA1) Gene Expression

The cholesterol efflux protein ATP binding cassette protein A1 (ABCA) and apolipoprotein A1 (apo A1) are key constituents in the process of reverse-cholesterol transport (RCT), whereby excess cholesterol in the periphery is transported to the liver where it can be converted primarily to bile acids for either use in digestion or excreted. Due to their essential roles in RCT, numerous studies have been conducted in cells, mice, and humans to more thoroughly understand the pathways that regulate their expression and activity with the goal of developing therapeutics that enhance RCT to reduce the risk of cardiovascular disease. Many of the drugs and natural compounds examined target several transcription factors critical for ABCA1 expression in both macrophages and the liver. Likewise, several miRNAs target not only ABCA1 but also the same transcription factors that are critical for its high expression. However, after years of research and many preclinical and clinical trials, only a few leads have proven beneficial in this regard. In this review we discuss the various transcription factors that serve as drug targets for ABCA1 and provide an update on some important leads.

Mechanistic roles of mutant p53 governing lipid metabolism

Metabolic reprogramming of cancer cells by various acquired mutations provides support for rapid proliferation and growth in the tumor microenvironment. Mutations in the TP53 gene are the most common mutation found across all human cancers. Commonly referred to as "the guardian of the genome", p53 has a well-established role as a tumor suppressor by mediating checkpoint integrity and protecting cells from DNA damage. To date, the many functional roles of p53 extending beyond its classical function and exerting control over metabolic processes continues to confound the field. Recently, emerging roles for p53 in mediating lipid metabolism have come to light with intriguing metabolic roles in regulating cholesterol homeostasis and lipid droplet formation. Herein, we will seek to unify the mechanisms by which absence of functional p53, as well as stable mutant forms of p53, exert control over these lipid metabolism programs. Of equal importance, synthetic lethal phenotypes in the context of mutant p53 and aberrant lipid homeostasis offer new possible targets in the therapeutic landscape. This review aims to characterize the mechanisms by which p53 exerts control over these pathways and examine how precision medicine may benefit from tumor subtyping of p53 mutations.

Dynamin-related protein 1 inhibition reduces hepatic PCSK9 secretion

AIMS

Proteostasis maintains protein homeostasis and participates in regulating critical cardiometabolic disease risk factors including proprotein convertase subtilisin/kexin type 9 (PCSK9). Endoplasmic reticulum (ER) remodeling through release and incorporation of trafficking vesicles mediates protein secretion and degradation. We hypothesized that ER remodeling that drives mitochondrial fission participates in cardiometabolic proteostasis.

METHODS AND RESULTS

We used in vitro and in vivo hepatocyte inhibition of a protein involved in mitochondrial fission, dynamin-related protein 1 (DRP1). Here, we show that DRP1 promotes remodeling of select ER microdomains by tethering vesicles at ER. A DRP1 inhibitor, mitochondrial division inhibitor 1 (mdivi-1) reduced ER localization of a DRP1 receptor, mitochondrial fission factor, suppressing ER remodeling-driven mitochondrial fission, autophagy, and increased mitochondrial calcium buffering and PCSK9 proteasomal degradation. DRP1 inhibition by CRISPR/Cas9 deletion or mdivi-1 alone or in combination with statin incubation in human hepatocytes and hepatocyte-specific Drp1-deficiency in mice reduced PCSK9 secretion (-78.5%). In HepG2 cells, mdivi-1 increased low-density lipoprotein receptor via c-Jun transcription and reduced PCSK9 mRNA levels via suppressed sterol regulatory binding protein-1c. Additionally, mdivi-1 reduced macrophage burden, oxidative stress, and advanced calcified atherosclerotic plaque in aortic roots of diabetic Apoe-deficient mice and inflammatory cytokine production in human macrophages.

CONCLUSIONS

We propose a novel tethering function of DRP1 beyond its established fission function, with DRP1-mediated ER remodeling likely contributing to ER constriction of mitochondria that drives mitochondrial fission. We report that DRP1-driven remodeling of select ER micro-domains may critically regulate hepatic proteostasis and identify mdivi-1 as a novel small molecule PCSK9 inhibitor.

Microbiota fermentation characteristics of acylated starches and the regulation mechanism of short-chain fatty acids on hepatic steatosis

Starches acylated with specific short-chain fatty acids (SCFAs) have the potential to provide specificity in SCFA delivery. It is well documented that SCFAs are involved in lipid metabolism, but the underlying mechanism is still unclear. For characterizing the fermentation properties of acylated starches with various SCFAs in terms of SCFA production, three different acylated starches were prepared following the esterification of high amylose maize starch (HAMS) using acetic anhydride, propionic anhydride and butyric anhydride, respectively. Compared with HAMS, the gut microbiota fermentation of acetylated, propionylated and butylated starches specifically increased the production of acetic acid, propionic acid, and butyric acid, respectively, indicating that the introduced acyl group can be effectively released during the fermentation process. Furthermore, the utilization of these starches generated more total SCFAs, suggesting that they can be effectively fermented by the microbiota as a carbohydrate substrate. Study on an in vitro model of cultured rat hepatocytes indicated that either mixed SCFAs or butyrate play an important role in regulating lipid metabolism via activating AMPK and PPAR signaling pathways, implying the importance of butyrate in the improvement of lipid metabolism and accumulation. This study may provide further understanding of the individual function of the corresponding SCFA.

ABCA7 links sterol metabolism to the host defense system: Molecular background for potential management measure of Alzheimer's disease

ATP-binding cassette transporter (ABC) A7 is a membrane protein that belongs to the large family of ABC transporters. It is 54% homologous in amino acid residue sequence to ABCA1 which mediates biogenesis of plasma high density lipoprotein (HDL) from cellular phospholipid and cholesterol with extracellular helical apolipoproteins such as apolipoprotein (apo) A-I. When transfected and expressed, ABCA7 also mediates generation of HDL-like particles but small and of less cholesterol content. However, endogenous ABCA7 is unlikely involved in HDL biogenesis and rather to regulate the host-defense system such as phagocytotic function of the cells. ABCA1 expression is regulated by cellular cholesterol levels, positively by the liver X receptor (LXR) in extrahepatic peripheral cells. However, it is modulated dually in the liver being relevant to transport of cholesterol for its catabolism; positively by LXR and negatively by sterol regulatory element binding protein (SREBP) or hepatic nuclear factor 4α (HNF4α). In contrast, ABCA7 expression was shown to be regulated negatively by the SREBP system so that decrease of cell cholesterol enhances ABCA7 function such as cellular phagocytotic reaction, suggesting that it links cholesterol metabolism to the host defense system. The interest is being build up in ABCA7 as its genomic diversity has been found related to a risk for late-onset Alzheimer's diseases. More recent findings indicate that ABCA7 is involved in metabolism of amyloid β peptide including its phagocytotic clearance. Accordingly, modulation of ABCA7 activity by manipulating cholesterol metabolism may open a new path for management of Alzheimer's disease.

Brothers in Arms: ABCA1- and ABCG1-Mediated Cholesterol Efflux as Promising Targets in Cardiovascular Disease Treatment

Atherosclerosis is a leading cause of cardiovascular disease worldwide, and hypercholesterolemia is a major risk factor. Preventive treatments mainly focus on the effective reduction of low-density lipoprotein cholesterol, but their therapeutic value is limited by the inability to completely normalize atherosclerotic risk, probably due to the disease complexity and multifactorial pathogenesis. Consequently, high-density lipoprotein cholesterol gained much interest, as it appeared to be cardioprotective due to its major role in reverse cholesterol transport (RCT). RCT facilitates removal of cholesterol from peripheral tissues, including atherosclerotic plaques, and its subsequent hepatic clearance into bile. Therefore, RCT is expected to limit plaque formation and progression. Cellular cholesterol efflux is initiated and propagated by the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1. Their expression and function are expected to be rate-limiting for cholesterol efflux, which makes them interesting targets to stimulate RCT and lower atherosclerotic risk. This systematic review discusses the molecular mechanisms relevant for RCT and ABCA1 and ABCG1 function, followed by a critical overview of potential pharmacological strategies with small molecules to enhance cellular cholesterol efflux and RCT. These strategies include regulation of ABCA1 and ABCG1 expression, degradation, and mRNA stability. Various small molecules have been demonstrated to increase RCT, but the underlying mechanisms are often not completely understood and are rather unspecific, potentially causing adverse effects. Better understanding of these mechanisms could enable the development of safer drugs to increase RCT and provide more insight into its relation with atherosclerotic risk. SIGNIFICANCE STATEMENT: Hypercholesterolemia is an important risk factor of atherosclerosis, which is a leading pathological mechanism underlying cardiovascular disease. Cholesterol is removed from atherosclerotic plaques and subsequently cleared by the liver into bile. This transport is mediated by high-density lipoprotein particles, to which cholesterol is transferred via ATP-binding cassette transporters ABCA1 and ABCG1. Small-molecule pharmacological strategies stimulating these transporters may provide promising options for cardiovascular disease treatment.

The Effects of Pitavastatin on Nuclear Factor-Kappa B and ICAM-1 in Human Saphenous Vein Graft Endothelial Culture

Objective

To study pitavastatin's effects on nuclear factor-kappa B (NF-κB ) and adhesion molecules in human saphenous vein graft endothelial culture indicating its pleotropic properties.

Materials and Method

Low-dose (0.1 μM/L) and high-dose (1μM/L) pitavastatin calcium were administered as a frontline therapy in human saphenous endothelial cell culture, followed by induction of inflammation by TNF-α and determination of mRNA level alterations of ICAM-1 and NF-κB genes of endothelial cells using the qRT-PCR method. Additionally, immunofluorescence method was used to show the expression of NF-κB and ICAM-1. Finally, LDH levels were determined by the ELISA method to quantify cytotoxicity.

Results

ICAM-1 mRNA expression in the low-dose pitavastatin+TNF-α group was significantly higher than that in the TNF-α group and significantly lower than that in the high-dose pitavastatin+TNF-α group (for all comparisons, P = 0.001). The low-dose pitavastatin+TNF-α group had a similar NF-κB mRNA expression with TNF-α and high-dose pitavastatin+TNF-α groups.

Conclusion

Pitavastatin increases ICAM-1 mRNA expression in saphenous vein endothelial cells. Furthermore, the effect of pitavastatin on adhesion molecules appears independent of NF-κB. Novel studies are needed in this field.

In-Situ imaging detection of cell membrane and intracellular cholesterol via cascade reactions

Herein, an effective membrane-to-intracellular cholesterol detection strategy was designed based on cascade reactions. A biochip array was firstly fabricated by consecutively immobilizing luminol modified gold nanoparticles (Au@luminol), soybean peroxidase (SBP) and cholesterol oxidase (ChoX) on the cellulose acetate (CA) membrane functionalized home-made micropore array. When cholesterol existed, it was oxidized by ChoX generating H₂O₂, which further triggered the CL reaction under the SBP catalysis, the CL signals were collected by a charge-coupled device (CCD). The proposed strategy exhibited a wide linear range from 0.12 μM to 1000 μM and relatively low detection limit (LOD) of 0.08 μM. Furthermore，it could be used to in-situ detect membrane cholesterol and intracelluar esterified cholesterol in HepG2 cells. After activated HepG2 cells were added to the modified biochip, membrane cholesterol was detected directly. Intracelluar esterified cholesterol was detected through the introduction of triton X-100 and cholesteryl esterase (ChoE). Additionally, the cholesterol content in cells was changed after stimulated by drugs, such as apolipoprotein A-I (ApoA-I), pitavastatin or probucol. The correlation of the CL signal with the amount of cholesterol confirmed that our strategy was feasible to simultaneously detect membrane and intracellular cholesterol at different cellular states. The proposed strategy exhibited excellent sensitivity, selectivity, stability, and reproducibility in a simple, cheap way, which opened a new door for studying clinic treatment of the cholesterol-related diseases.

Association between familial hypobetalipoproteinemia and the risk of diabetes. Is this the other side of the cholesterol-diabetes connection? A systematic review of literature

Statin therapy is beneficial in reducing LDL cholesterol (LDL-C) levels and cardiovascular events, but it is associated with the risk of incident diabetes mellitus (DM). Familial hypercholesterolemia (FH) is characterized by genetically determined high levels of plasma LDL-C and a low prevalence of DM. LDL-C levels seem then inversely correlated with prevalence of DM. Familial hypobetalipoproteinemia (FHBL) represents the genetic mirror of FH in terms of LDL-C levels, very low in subjects carrying mutations of APOB, PCSK9 (FHBL1) or ANGPTL3 (FHBL2). This review explores the hypothesis that FHBL might represent also the genetic mirror of FH in terms of prevalence of DM and that it is expected to be increased in FHBL in comparison with the general population. A systematic review of published literature on FHBL was made by searching PubMed (1980-2016) for articles presenting clinical data on FHBL probands and relatives. The standardized prevalence rates of DM in FHBL1 were similar to those of the reference population, with a prevalence rate of 8.2 and 9.2%, respectively, while FHBL2 showed a 4.9% prevalence of DM. In conclusion, low LDL-C levels of FHBL do not seem connected to DM as it happens in subjects undergoing statin therapy and the diabetogenic effect of statins has to be explained by mechanisms that do not rely exclusively on the reduced levels of LDL-C. The review also summarizes the published data on the effects of FHBL on insulin sensitivity and the relationships between FH, statin therapy, FHBL1 and intracellular cholesterol metabolism, evaluating possible diabetogenic pathways.

Serum CETP status is independently associated with reduction rates in LDL-C in pitavastatin-treated diabetic patients and possible involvement of LXR in its association

BACKGROUND

Statins decrease cholesteryl ester transfer protein (CETP) levels, which have been positively associated with hepatic lipid content as well as serum low density lipoproteins-cholesterol (LDL-C) levels. However, the relationship between the CETP status and statin-induced reductions in LDL-C levels has not yet been elucidated in detail. We herein examined the influence of the CETP status on the lipid-reducing effects of pitavastatin in hypercholesterolemic patients with type 2 diabetes mellitus as well as the molecular mechanism underlying pitavastatin-induced modifications in CETP levels.

METHODS

Fifty-three patients were treated with 2 mg of pitavastatin for 3 months. Serum levels of LDL-C, small dense (sd) LDL-C, and CETP were measured before and after the pitavastatin treatment. The effects of pitavastatin, T0901317, a specific agonist for liver X receptor (LXR) that reflects hepatic cholesterol contents, and LXR silencing on CETP mRNA expression in HepG2 cells were also examined by a real-time PCR assay.

RESULTS

The pitavastatin treatment decreased LDL-C, sdLDL-C, and CETP levels by 39, 42, and 23%, respectively. Despite the absence of a significant association between CETP and LDL-C levels at baseline, baseline CETP levels and its percentage change were an independent positive determinant for the changes observed in LDL-C and sdLDL-C levels. The LXR activation with T0901317 (0.5 μM), an in vitro condition analogous to hepatic cholesterol accumulation, increased CETP mRNA levels in HepG2 cells by approximately 220%, while LXR silencing markedly diminished the increased expression of CETP. Pitavastatin (5 μM) decreased basal CETP mRNA levels by 21%, and this was completely reversed by T0901317.

CONCLUSION

Baseline CETP levels may predict the lipid-reducing effects of pitavastatin. Pitavastatin-induced CETP reductions may be partially attributed to decreased LXR activity, predictable by the ensuing decline in hepatic cholesterol synthesis.

TRIAL REGISTRATION

UMIN Clinical Trials Registry ID UMIN000019020.

Risk of diabetes in patients treated with HMG-CoA reductase inhibitors

OBJECTIVE

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) are used to control blood cholesterol levels and reduce cardiovascular disease. It has been repeatedly reported that statins may cause new-onset diabetes mellitus (DM). However, limited evidence exists from direct head to head comparisons of statins on whether the risk of DM differs among statins. We investigated the risk of development of new-onset diabetes in subjects treated with different statins.

METHODS

We retrospectively enrolled consecutive 3680 patients without DM or impaired fasting glucose who started receiving statin treatment for cholesterol control. We evaluated the incidence of new-onset diabetes according to the type of statin.

RESULTS

The mean duration of follow-up was 62.6±15.3 months. The incidence of DM was significantly higher in the pitavastatin group (49 of 628; 7.8%) compared to that in the other statin groups [atorvastatin (68 of 1327; 5.1%), rosuvastatin (77 of 1191; 6.5%), simvastatin (11 of 326; 3.4%), and pravastatin (12 of 298; 5.8%); p=0.041]. The risk of diabetes was the highest in the pitavastatin group compared with that in the simvastatin group [hazard ratio (HR)=2.68, p=0.011]. Other statins showed no significant risk differences compared to that for simvastatin. Fasting blood glucose (FBG) level at baseline and body-mass index (BMI) were associated with the development of diabetes [FBG, HR=1.11, p<0.001; BMI, HR=1.02, p=0.005].

CONCLUSIONS

Among the five statins, pitavastatin showed the strongest effect on the development of new-onset diabetes.

SREBP-1 has a prognostic role and contributes to invasion and metastasis in human hepatocellular carcinoma

Sterol regulatory element-binding protein 1 (SREBP-1) is a well-known nuclear transcription factor involved in lipid synthesis. Recent studies have focused on its functions in tumor cell proliferation and apoptosis, but its role in cell migration and invasion, especially in hepatocellular carcinoma (HCC), is still unclear. In this study, we found that the expression of SREBP-1 in HCC tissues was significantly higher than those in matched tumor-adjacent tissues (p < 0.05). SREBP-1 was expressed at significantly higher levels in patients with large tumor size, high histological grade and advanced tumor-node-metastasis (TNM) stage (p < 0.05). The positive expression of SREBP-1 correlated with a worse 3-year overall and disease-free survival of HCC patients (p < 0.05). Additionally, SREBP-1 was an independent factor for predicting both 3-year overall and disease-free survival of HCC patients (p < 0.05). In vitro studies revealed that downregulation of SREBP-1 inhibited cell proliferation and induced apoptosis in both HepG2 and MHCC97L cells (p < 0.05). Furthermore, wound healing and transwell assays showed that SREBP-1 knockdown prominently inhibited cell migration and invasion in both HepG2 and MHCC97L cells (p < 0.05). These results suggest that SREBP-1 may serve as a prognostic marker in HCC and may promote tumor progression by promoting cell growth and metastasis.

Inter-organ communication in the regulation of lipid metabolism: focusing on the network between the liver, intestine, and heart

Recent studies have shown that lipid metabolism is regulated through the orchestration of multiple organs. Gut microbiota influences the metabolism of the liver through the production of fatty acids and phosphatidylcholine as well as the modulation of bile acid profile. Microbiota also affects the cardiovascular system through the production of metabolites from nutrients. MicroRNAs (miRNAs) are non-coding RNAs comprised of around 22 nucleotides in length. MiRNAs are released into blood flow from organs and interfere with the gene expression of target organs. MiRNAs are involved in the regulation of metabolic homeostasis including lipoprotein production and cardiovascular functions. Fatty acids are also circulating and distributed to each organ by fatty acid transporting proteins. Fatty acids can act as a ligand of G protein-coupled receptors, such as GPR41 and GPR43, and nuclear receptor PPARα, which bear crucial roles in the regulation of energy expenditure. Therefore the inter-organ communication plays important roles in the systematic regulation of lipid metabolism. Studies on the inter-organ network system will contribute to the development of diagnostic and therapeutic strategies for metabolic diseases. This review discusses how lipid metabolism is regulated by the inter-organ communication, focusing on the network axis between the liver, intestine, and heart.

Statins and lipid metabolism: an update

PURPOSE OF REVIEW

The reduction in cardiovascular disease risk by statins is well established. This risk reduction has mostly been attributed to decreases in plasma LDL cholesterol and other pleiotropic effects of statins. Emerging evidence indicates that statins exert multiple effects on lipoprotein metabolism, including chylomicrons and HDLs.

RECENT FINDINGS

Kinetic and in-vitro studies have documented that the effects of statins on the metabolism of different lipoproteins are for the most part the direct consequence of cholesterol biosynthesis inhibition and the subsequent change in transcription factors and cell signaling, regulating different aspects of lipoprotein metabolism. Differences in pharmacokinetics and pharmacodynamics among statins lead to diverse biological outcomes.

SUMMARY

The current review summarizes recent experimental evidence highlighting the different effects of statins on cellular pathways regulating gene expression. Understanding the basic mechanisms by which different statins regulate lipoprotein metabolism will lead to improved strategies for the prevention and treatment of specific lipoprotein disorders.

Pleiotropic effects of pitavastatin

3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are established first line treatments for hypercholesterolaemia. In addition to the direct effects of statins in reducing concentrations of atherogenic low density lipoprotein cholesterol (LDL-C), several studies have indicated that the beneficial effects of statins may be due to some of their cholesterol-independent, multiple (pleiotropic) effects which may differ between different members of the class. Pitavastatin is a novel synthetic lipophilic statin that has a number of pharmacodynamic and pharmacokinetic properties distinct from those of other statins, which may underlie its potential pleiotropic benefits in reducing cardiovascular risk factors. This review examines the principal pleiotropic effects of pitavastatin on endothelial function, vascular inflammation, oxidative stress and thrombosis. The article is based on a systematic literature search carried out in December 2010, together with more recent relevant publications where appropriate. The available data from clinical trials and in vitro and animal studies suggest that pitavastatin is not only effective in reducing LDL-C and triglycerides, but also has a range of other effects. These include increasing high density lipoprotein cholesterol, decreasing markers of platelet activation, improving cardiac, renal and endothelial function, and reducing endothelial stress, lipoprotein oxidation and, ultimately, improving the signs and symptoms of atherosclerosis. It is concluded that the diverse pleiotropic actions of pitavastatin may contribute to reducing cardiovascular morbidity and mortality beyond that achieved through LDL-C reduction.

Cholesterol-lowering therapy for the treatment of nonalcoholic fatty liver disease: an update

PURPOSE OF REVIEW

To review recent human trials assessing cholesterol-lowering agents in nonalcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

Four randomized controlled trials (RCTs) assessed statins in NAFLD. In the only RCT with post-treatment biopsy, simvastatin did not change liver histology. In the remaining RCTs, atorvastatin was well tolerated, significantly improved radiological/biochemical markers of steatosis and plasma lipids, with neutral effects on glucose metabolism; in the Greek Atorvastatin and Coronary Heart Disease Evaluation (GREACE) study, atorvastatin reduced incident cardiovascular disease compared with both untreated NAFLD patients and with statin-treated patients without NAFLD. Ezetimibe was evaluated in two uncontrolled trials and two RCTs, consistently improving liver histology and plasma lipids, whereas glucose metabolism was generally unaffected; however, HbA1c increased with ezetimibe in one RCT.

SUMMARY

From the analysis of available trials, it emerges that cholesterol-lowering agents may considerably benefit NAFLD patients. Statins are well tolerated, and atorvastatin improved surrogate markers of liver disease, whereas their effect on liver histology is unknown. Furthermore, the GREACE study was the first trial to show clinical benefit from the use of a pharmacological agent in NAFLD. Ezetimibe improved liver histology. The benefit of combination therapy, as well as the safety on glucose metabolism, need further evaluation.