Targeting high-density lipoproteins: Update on a promising therapy

HDL Composition, Heart Failure, and Its Comorbidities

Although research on high-density lipoprotein (HDL) has historically focused on atherosclerotic coronary disease, there exists untapped potential of HDL biology for the treatment of heart failure. Anti-oxidant, anti-inflammatory, and endothelial protective properties of HDL could impact heart failure pathogenesis. HDL-associated proteins such as apolipoprotein A-I and M may have significant therapeutic effects on the myocardium, in part by modulating signal transduction pathways and sphingosine-1-phosphate biology. Furthermore, because heart failure is a complex syndrome characterized by multiple comorbidities, there are complex interactions between heart failure, its comorbidities, and lipoprotein homeostatic mechanisms. In this review, we will discuss the effects of heart failure and associated comorbidities on HDL, explore potential cardioprotective properties of HDL, and review novel HDL therapeutic targets in heart failure.

Mimic Lipoproteins Responsive to Intratumoral pH and Allosteric Enzyme for Efficient Tumor Therapy

Discoid-reconstituted high-density lipoprotein (d-rHDL) is advantageous for tumor-targeted drug delivery due to its small size, long circulation, and efficient internalization into cancer cells. Nevertheless, an allosteric reaction catalyzed by serum lecithin-cholesterol acyltransferase (LCAT) may cause drug leakage from d-rHDL and reduce its targeting efficiency. Conversely, similar "structural weakening" catalyzed by acyl-coenzyme A-cholesterol acyltransferase (ACAT) inside tumor cells can stimulate precise intracellular drug release. Therefore, we synthesized and characterized a pH-sensitive n-butyraldehyde bi-cholesterol (BCC) to substitute for cholesterol in the d-rHDL particle, and bovine serum albumin (BSA) was used as the targeting agent. This dual pH- and ACAT-sensitive d-rHDL (d-d-rHDL) was small with a disk-like appearance. Morphological transformation observation, in vitro release assays, and differences in internalization upon LCAT treatment confirmed that BCC effectively inhibited the remodeling behavior and enhanced the tumor-targeting efficiency. The accumulation of d-d-rHDL in HepG2 cells was significantly higher than that in LO2 cells, and accumulation was inhibited by free BSA. The pH sensitivity was verified, and d-d-rHDL achieved efficient drug release in vitro and inside tumor cells after exposure to acidic conditions and ACAT. Confocal laser scanning microscopy demonstrated that d-d-rHDL escaped from lysosomes and became distributed evenly throughout cells. Moreover, in vivo imaging assays in a tumor-bearing mouse model demonstrated tumor-targeting properties of d-d-rHDL, and paclitaxel-loaded d-d-rHDL showed strong anticancer activity in these mice. This dual-sensitive d-d-rHDL thus combines structural stability in plasma and an intracellular pH/ACAT-triggered drug release to facilitate inhibition of tumor growth.

Adenosine Diphosphate and the P2Y13 Receptor Are Involved in the Autophagic Protection of Ex Vivo Perfused Livers From Fasted Rats: Potential Benefit for Liver Graft Preservation

Studies on how to protect livers perfused ex vivo can help design strategies for hepatoprotection and liver graft preservation. The protection of livers isolated from 24-hour versus 18-hour starved rats has been previously attributed to autophagy, which contributes to the energy-mobilizing capacity ex vivo. Here, we explored the signaling pathways responsible for this protection. In our experimental models, 3 major signaling candidates were considered in view of their abilities to trigger autophagy: high mobility group box 1 (HMGB1), adenosine monophosphate-activated protein kinase (AMPK), and purinergic receptor P2Y13. To this end, ex vivo livers isolated from starved rats were perfused for 135 minutes, after which perfusate samples were studied for protein release and biopsies were performed for evaluating signaling protein contents. For HMGB1, no significant difference was observed between livers isolated from rats starved for 18 and 24 hours at perfusion times of both 0 and 135 minutes. The phosphorylated and total forms of AMPK, but not their ratios, were significantly higher in 24-hour fasted than in 18-hour fasted livers. However, although the level of phosphorylated AMPK increased, perfusing ex vivo 18-hour fasted livers with 1 mM 5-aminoimidazole-4-carboxamide ribonucleotide, an AMPK activator, did not protect the livers. In addition, the adenosine diphosphate (ADP; and not adenosine monophosphate [AMP]) to AMP + ADP + adenosine triphosphate ratio increased in the 24-hour starved livers compared with that in the 18-hour starved livers. Moreover, perfusing 24-hour starved livers with 0.1 mM 2-[(2-chloro-5-nitrophenyl)azo]-5-hydroxy-6-methyl-3-[(phosphonooxy)methyl]-4-pyridinecarboxaldehyde (MRS2211), a specific antagonist of the P2Y13 receptor, induced an increase in cytolysis marker levels in the perfusate samples and a decrease in the levels of autophagic marker microtubule-associated proteins 1 light chain 3 II (LC3II)/actin (and a loss of p62/actin decrease), indicating autophagy inhibition and a loss of protection. The P2Y13 receptor and ADP (a physiological activator of this receptor) are involved in the protection of ex vivo livers. Therapeutic opportunities for improving liver graft preservation through the stimulation of the ADP/P2Y13 receptor axis are further discussed.

Case study-based systematic review of literature on lymphoma-associated cardiac tamponade

This study aimed to compile all the relevant studies of patients presenting with pericardial tamponade before or after diagnosis of lymphoma, describe the clinical presentations of patients with lymphoma and cardiac tamponade, and assess the difference in overall survival based on the timing of cardiac tamponade diagnosis.

A comprehensive search strategy was conducted in the following databases: PubMed and Cochrane Library, using the following keywords: Lymphoma AND Cardiac Tamponade. The criteria for eligibility included cases with a confirmed diagnosis of lymphoma and cardiac tamponade, human studies, and publications in English language. The statistical analysis was performed using IBM Statistical Package for Social Sciences (SPSS) version 20. We included 48 research articles (n = 52 cases) with adequate reporting of measured outcomes. The median age of the patients was 52 (9–94) years. Only 6 patients were noted to have primary cardiac lymphoma, while the majority of cases were considered to have secondary cardiac lymphoma (88.5%). According to the data on the type of lymphoma reported through cytology and immunohistochemistry, 49 patients were diagnosed with non-Hodgkin lymphoma, and of these cases the most common subtype was large B-cell lymphoma (42.9%). Overall, the average duration of illness was 14 ± 23 days. A total of 13 patients had distant heart sounds, 12 cases were noted to be hypotensive, and 13 subjects were found to have increased jugular venous pressure.

Our retrospective study demonstrated that most patients presented with pericardial tamponade after lymphoma diagnosis, and those were mostly secondary cardiac lymphoma of the non-Hodgkin type with large B-cell as the most common subtype. Dyspnoea, oedema, and constitutional symptoms were the most common presenting signs. The median overall survival of patients with lymphoma and cardiac tamponade is 4 months, with no significant difference in mortality in the presentation timing before and after the diagnosis of lymphoma.

Nuclear receptors, gestational metabolism and maternal metabolic disorders

Normal pregnancy is characterised by a gradual alteration in metabolism that results in elevated serum bile acids, dyslipidaemia and impaired glucose tolerance in the third trimester. Nuclear receptors play important roles in regulating metabolic pathways that influence alterations in these parameters. There is evidence for altered function of FXR and LXR in gestation; these nuclear receptors play an integral role in bile acid and lipid homeostasis. There is some evidence for influence of clock genes in late pregnancy metabolic changes, and this may be linked to alterations in placental gene expression and function, thereby influencing fetal growth. This article will review the current data from human studies and investigation of animal models to illustrate the role of nuclear receptors (namely LXR, FXR, PPARs and clock genes) in gestational alterations in metabolism and the ways this may influence susceptibility to metabolic disorders of pregnancy such as gestational diabetes mellitus and intrahepatic cholestasis of pregnancy.

Lipoprotein-Inspired Nanocarrier Composed of Folic Acid-Modified Protein and Lipids: Preparation and Evaluation of Tumor-Targeting Effect

Background

Reconstituted lipoproteins (rLips) based on endogenous lipid nanostructures has been increasingly regarded as an excellent and promising antitumor drug delivery. However, some problems relating to the main component, apolipoprotein, for instance, rare source, unaffordable price, and low specificity of relevant receptor expression, become chief obstacles to its broad development and application.

Purpose

The primary aim of this study is to develop biomimetic rLips by utilizing folic acid (FA)-modified bovine serum albumin (BSA) as a replacement for apolipoprotein and demonstrate its tumor targeting and antitumor efficacy.

Methods

The amino groups of BSA were covalently conjugated with FA through the amide reaction. PTX-loaded nanostructured lipid carrier (termed as P-NLC) consisting of phospholipid, cholesteryl ester, triglyceride and cholesterol was prepared by the emulsification–evaporation method and utilized as the lipid core. FA-modified BSA (FA-BSA) was characterized for the protein substitute degree and attached with NLC by incubation-insert method to form the lipoprotein-mimic nanocomplex (termed as PFB-rLips). The morphology of nanoparticles was observed under transmission electron microscopy (TEM), and the particle size and zeta potential were determined using dynamic light scattering. In vitro release behavior of PTX from PFB-rLips was investigated with the dialysis method. Hemolysis tests were conducted to evaluate the biosecurity of PFB-rLips. Cell uptake and cytotoxicity assays were performed on human hepatocytes (LO2) and human hepatoma cells (HepG2). Tumor targeting was assessed using in vivo imaging system in H22 tumor-bearing mice model. Antitumor efficacy in vivo was investigated and compared between Taxol^® (paclitaxel) formulation and PTX-incorporated nanoparticles in the same tumor model.

Results

A fixed molar ratio 50:1 of FA to BSA was chosen as the optimal input ratio based on the balance between appropriate degree of protein substitution and amphiphilicity of FA-BSA. The morphology of FB-rLips exhibited as a homogeneous spherical structure featured by lipid cores surrounded with a cloudy protein shell observed under TEM. The particle size, zeta potential and encapsulation efficiency were 174.6±3.2 nm, −17.26±0.9 mV and 82.2±2.4%, respectively. In vitro release behavior of PTX from PFB-rLips was slow and sustained. The uptake of FB-rLips was much higher in HepG2 cells than in LO2 cells. Furthermore, the uptake of FB-rLips was significantly higher than that of rLips without FA involved (termed as B-rLips) and NLC in HepG2 cells. Hemolysis and cytotoxicity assays showed good biocompatibility of FB-rLips. The internalization mechanism of FB-rLips mainly depended on clathrin-mediated and caveolin-mediated endocytosis coupling with energy consumption, and FA receptors expressed on tumor cells played a critical role in cellular uptake process. CCK-8 studies demonstrated that PFB-rLips exhibited significantly better tumor killing ability than Taxol^® (paclitaxel) formulation in vitro. Moreover, FB-rLips produced more excellent tumor-targeting properties than NLC through in vivo imaging assays. On the basis of this, PTX-loaded FB-rLips also performed more remarkable anticancer activity than other therapy groups in H22 tumor-bearing mice.

Conclusion

FB-rLips would serve as a potential nanocarrier for improving tumor-targeting and therapeutic efficacy while reducing the side effects on normal tissues and organs.

Synthesis, biological evaluation and SAR studies of ursolic acid 3β-ester derivatives as novel CETP inhibitors

Cholesteryl ester transfer protein (CETP) is an attractive therapeutic target for the prevention and treatment of cardiovascular diseases by lowering low-density lipoprotein cholesterol levels as well as raising high-density lipoprotein cholesterol levels in human plasma. Herein, a series of ursolic acid 3β-ester derivatives were designed, synthesized and evaluated for the CETP inhibiting activities. Among these compounds, the most active compound is U12 with an IC50 value of 2.4 μM in enzymatic assay. The docking studies showed that the possible hydrogen bond interactions between the carboxyl groups at both ends of the molecule skeleton and several polar residues (such as Ser191, Cys13 and Ser230) in the active site region of CETP could significantly enhance the inhibition activity. This study provides structural insight of the interactions between these pentacyclic triterpenoid 3β-ester derivatives and CETP protein for the further modification and optimization.

Serum inhibitory factor 1, high-density lipoprotein and cardiovascular diseases

PURPOSE OF REVIEW

The atheroprotective properties of HDL are supported by epidemiological and preclinical research. However, the results of interventional trials paradoxically indicate that drugs increasing HDL-cholesterol (HDL-C) do not reduce coronary artery disease (CAD) risk. Moreover, Mendelian randomization studies have shown no effect of HDL-C-modifying variants on CAD outcome. Thus, the protective effects of HDL particles are more governed by their functional status than their cholesterol content. In this context, any successful clinical exploitation of HDL will depend on the identification of HDL-related biomarkers, better than HDL-C level, for assessing cardiovascular risk and monitoring responses to treatment.

RECENT FINDINGS

Recent studies have enlightened the role of ecto-F1-ATPase as a cell surface receptor for apoA-I, the major apolipoprotein of HDL, involved in the important metabolic and vascular atheroprotective functions of HDL. In the light of these findings, the clinical relevance of ecto-F1-ATPase in humans has recently been supported by the identification of serum F1-ATPase inhibitor (IF1) as an independent determinant of HDL-C, CAD risk and cardiovascular mortality in CAD patients.

SUMMARY

Serum IF1 measurement might be used as a novel HDL-related biomarker to better stratify risk in high-risk populations or to determine pharmacotherapy.

Camphene, a Plant Derived Monoterpene, Exerts Its Hypolipidemic Action by Affecting SREBP-1 and MTP Expression

The control of hyperlipidemia plays a central role in cardiovascular disease. Previously, we have shown that camphene, a constituent of mastic gum oil, lowers cholesterol and triglycerides (TG) in the plasma of hyperlipidemic rats without affecting HMG-CoA reductase activity, suggesting that its hypocholesterolemic and hypotriglyceridemic effects are associated with a mechanism of action different than that of statins. In the present study, we examine the mechanism by which camphene exerts its hypolipidemic action. We evaluated the effect of camphene on the de novo synthesis of cholesterol and TG from [14C]-acetate in HepG2 cells, along with the statin mevinolin. Camphene inhibited the biosynthesis of cholesterol in a concentration-dependent manner, and a maximal inhibition of 39% was observed at 100 μM while mevinolin nearly abolished cholesterol biosynthesis. Moreover, treatment with camphene reduced TG by 34% and increased apolipoprotein AI expression. In contrast, mevinolin increased TG by 26% and had a modest effect on apolipoprotein AI expression. To evaluate the mode of action of camphene, we examined its effects on the expression of SREBP-1, which affects TG biosynthesis and SREBP-2, which mostly affects sterol synthesis. Interestingly, camphene increased the nuclear translocation of the mature form of SREBP-1 while mevinolin was found to increase the amount of the mature form of SREBP-2. The effect of camphene is most likely regulated through SREBP-1 by affecting MTP levels in response to a decrease in the intracellular cholesterol. We propose that camphene upregulates SREBP-1 expression and MTP inhibition is likely to be a probable mechanism whereby camphene exerts its hypolipidemic effect.

Lipoprotein profiles in human heterozygote carriers of a functional mutation P297S in scavenger receptor class B1

The scavenger receptor class B type 1 (SR-B1) is an important HDL receptor involved in cholesterol uptake and efflux, but its physiological role in human lipoprotein metabolism is not fully understood. Heterozygous carriers of the SR-B1(P297S) mutation are characterized by increased HDL cholesterol levels, impaired cholesterol efflux from macrophages and attenuated adrenal function. Here, the composition and function of lipoproteins were studied in SR-B1(P297S) heterozygotes.Lipoproteins from six SR-B1(P297S) carriers and six family controls were investigated. HDL and LDL/VLDL were isolated by ultracentrifugation and proteins were separated by two-dimensional gel electrophoresis and identified by mass spectrometry. HDL antioxidant properties, paraoxonase 1 activities, apoA-I methionine oxidations and HDL cholesterol efflux capacity were assessed.Multivariate modeling separated carriers from controls based on lipoprotein composition. Protein analyses showed a significant enrichment of apoE in LDL/VLDL and of apoL-1 in HDL from heterozygotes compared to controls. The relative distribution of plasma apoE was increased in LDL and in lipid-free form. There were no significant differences in paraoxonase 1 activities, HDL antioxidant properties or HDL cholesterol efflux capacity but heterozygotes showed a significant increase of oxidized methionines in apoA-I.The SR-B1(P297S) mutation affects both HDL and LDL/VLDL protein compositions. The increase of apoE in carriers suggests a compensatory mechanism for attenuated SR-B1 mediated cholesterol uptake by HDL. Increased methionine oxidation may affect HDL function by reducing apoA-I binding to its targets. The results illustrate the complexity of lipoprotein metabolism that has to be taken into account in future therapeutic strategies aiming at targeting SR-B1.

Low High-Density Lipoprotein and Risk of Myocardial Infarction

Low HDL is an independent risk factor for myocardial infarction. This paper reviews our current understanding of HDL, HDL structure and function, HDL subclasses, the relationship of low HDL with myocardial infarction, HDL targeted therapy, and clinical trials and studies. Furthermore potential new agents, such as alirocumab (praluent) and evolocumab (repatha) are discussed.

Increased atherosclerosis in P2Y13/apolipoprotein E double-knockout mice: contribution of P2Y13 to reverse cholesterol transport

AIMS

High-density lipoproteins (HDLs) protect against atherosclerosis mainly due to their function in hepatobiliary reverse cholesterol transport (RCT). This is a process whereby excess cholesterol from peripheral tissues is transported by HDL particles to the liver for further metabolism and biliary excretion. Hepatic uptake of HDL holoparticles involves the P2Y13 receptor, independently of the selective cholesteryl ester uptake mediated by scavenger receptor class B, type I (SR-BI). Accordingly, P2Y13-deficient mice (P2Y13 (-/-)) have impaired RCT. This study assessed whether P2Y13 deficiency would affect atherosclerotic development.

METHODS AND RESULTS

P2Y13 (-/-) mice were crossbred with atherosclerosis-prone apoE(-/-) mice. When 15 weeks old, P2Y13 (-/-)/apoE(-/-) mice had more aortic sinus lesions than apoE(-/-) mice. Bone marrow transplantation showed that the absence of the P2Y13 receptor in blood cells did not lead to significantly greater atherosclerotic plaque size formation compared with control apoE(-/-) reconstituted animals. Conversely, the absence of the P2Y13 receptor, except in blood cells, resulted in lesion sizes similar to that in P2Y13 (-/-)/apoE(-/-) reconstituted mice, pointing to a role for non-haematopoietic-derived P2Y13. Unexpectedly, P2Y13 (-/-)/apoE(-/-) mice displayed a lower HDL-cholesterol level than apoE(-/-) mice, which might be due to greater SR-BI expression in the liver. However, P2Y13 deficiency in apoE(-/-) mice was translated into reduced biliary and faecal sterol excretion and impaired RCT from macrophage to faeces, suggesting that an alteration in hepatobiliary RCT could be solely responsible for the greater atherosclerosis observed.

CONCLUSION

The P2Y13 receptor protects against atherosclerosis, primarily through its role in hepatobiliary RCT.

Looking into the Crystal Ball—Upcoming Drugs for Dyslipidemia

Dyslipidaemia is a critical risk factor for the development of cardiovascular complications such as ischemic heart disease and stroke. Although statins are effective anti-dyslipidemic drugs, their usage is fraught with issues such as failure of adequate lipid control in 30% of cases and intolerance in select patients. The limited potential of other alternatives such as fibrates, bile acid sequestrants and niacin has spurred the search for novel drug molecules with better efficacy and safety. CETP inhibitors such as evacetrapib and anacetrapib have shown promise in raising HDL besides LDL lowering property. Microsomal triglyceride transfer protein (MTP) inhibitors such as lomitapide and Apo CIII inhibitors such as mipomersen have recently been approved in Familial Hypercholesterolemia but experience in the non-familial setting is pretty much limited. One of the novel anti-dyslipidemic drugs which is greatly anticipated to make a mark in LDL-C control is the PCSK9 inhibitors. Some of the anti-dyslipidemic drugs which work by PCSK9 inhibition include evolocumab, alirocumab and ALN-PCS. Other approaches that are being given due consideration include farnesoid X receptor modulation and Lp-PLA2 inhibition. While it may not be an easy proposition to dismantle statins from their current position as a cholesterol reducing agent and as a drug to reduce coronary and cerebro-vascular atherosclerosis, our improved understanding of the disease and appropriate harnessing of resources using sound and robust technology could make rapid in-roads in our pursuit of the ideal anti-dyslipidemic drug.

A review on the traditional Chinese medicinal herbs and formulae with hypolipidemic effect

Hyperlipidemia, characterized by the abnormal blood lipid profiles, is one of the dominant factors of many chronic diseases such as diabetes, obesity, and cardiovascular diseases (CVD). For the low cost, effectiveness, and fewer side effects, the popularity of using traditional Chinese medicine (TCM) to handle hyperlipidemia is increasing and its role in health care has been recognized by the public at large. Despite the importance of TCM herbs and formulations, there is no comprehensive review summarizing their scientific findings on handling hyperlipidemia. This review summarizes the recent experimental and clinical results of nine representative single Chinese herbs and seven classic TCM formulae that could improve lipid profiles so as to help understand and compare their underlying mechanisms. Most of single herbs and formulae demonstrated the improvement of hyperlipidemic conditions with multiple and diverse mechanisms of actions similar to conventional Western drugs in spite of their mild side effects. Due to increasing popularity of TCM, more extensive, well-designed preclinical and clinical trials on the potential synergistic and adverse side effects of herb-drug interactions as well as their mechanisms are warranted. Hyperlipidemic patients should be warned about the potential risks of herb-drug interactions, particularly those taking anticoagulants and antiplatelet drugs.