Seeking Novel Targets for Improving In Vivo Macrophage-Specific Reverse Cholesterol Transport: Translating Basic Science into New Therapies for the Prevention and Treatment of Atherosclerosis

Current Therapies Focused on High-Density Lipoproteins Associated with Cardiovascular Disease

High-density lipoproteins (HDL) comprise a heterogeneous family of lipoprotein particles divided into subclasses that are determined by density, size and surface charge as well as protein composition. Epidemiological studies have suggested an inverse correlation between High-density lipoprotein-cholesterol (HDL-C) levels and the risk of cardiovascular diseases and atherosclerosis. HDLs promote reverse cholesterol transport (RCT) and have several atheroprotective functions such as anti-inflammation, anti-thrombosis, and anti-oxidation. HDLs are considered to be atheroprotective because they are associated in serum with paraoxonases (PONs) which protect HDL from oxidation. Polyphenol consumption reduces the risk of chronic diseases in humans. Polyphenols increase the binding of HDL to PON1, increasing the catalytic activity of PON1. This review summarizes the evidence currently available regarding pharmacological and alternative treatments aimed at improving the functionality of HDL-C. Information on the effectiveness of the treatments has contributed to the understanding of the molecular mechanisms that regulate plasma levels of HDL-C, thereby promoting the development of more effective treatment of cardiovascular diseases. For that purpose, Scopus and Medline databases were searched to identify the publications investigating the impact of current therapies focused on high-density lipoproteins.

Toll-like receptor 2 downregulates the cholesterol efflux by activating the nuclear factor-κB pathway in macrophages and may be a potential therapeutic target for the prevention of atherosclerosis

Atherosclerosis is a chronic inflammatory disease, which is triggered by lipid retention. Toll-like receptor 2 (TLR2) is a novel target for therapeutic intervention in atherosclerosis. In addition, nuclear factor-κB (NF-κB) serves important roles in stress response and inflammation. The present study investigated whether TLR2 is involved in the activation of cholesterol efflux in macrophages by regulating the NF-κB pathway. The human monocytic THP-1 cell line and murine macrophage RAW264.7 cell line were treated with 50 µg/ml oxidized low-density lipoprotein (ox-LDL) for 48 h in order to obtain macrophage foam cells. The cholesterol efflux of the cell lines under exogenous TLR2 treatment was assessed by liquid scintillation counting. Furthermore, the protein and mRNA expression levels of ATP binding cassette transporter A1 (ABCA1), ABCG1 and scavenger receptor B1 (SR-B1) were examined by western blot and quantitative polymerase chain reaction assays, respectively. To detect the effect of NF-κB on cholesterol efflux, the cells were divided into three groups, including the control, 10 ng/ml lipopolysaccharides (LPS; 24 h) and 10 ng/ml LPS + 50 µM pyrrolidinedithiocarbamate (PDTC; 24 h) groups. The results indicated that ox-LDL induced foam cell formation in the THP-1 and RAW264.7 cells, while TLR2 significantly decreased the cholesterol efflux in dose- and time-dependent manners. Accordingly, TLR2 reduced ABCA1, ABCG1 and SR-B1 expression at the transcriptional and translational levels in a dose-dependent manner. In addition, application of PDTC (an NF-κB specific inhibitor) markedly suppressed the LPS-induced downregulation of cholesterol efflux. These data revealed that TLR2 may be involved in the activation of cholesterol efflux in macrophages by regulating the NF-κB signaling pathway.

DBZ (Danshensu Bingpian Zhi), a Novel Natural Compound Derivative, Attenuates Atherosclerosis in Apolipoprotein E-Deficient Mice

BACKGROUND

DBZ (Danshensu Bingpian Zhi), a synthetic derivative of a natural compound found in traditional Chinese medicine, has been reported to suppress lipopolysaccharide-induced macrophage activation and lipid accumulation in vitro. The aim of this study was to assess whether DBZ could attenuate atherosclerosis at early and advanced stages.

METHODS AND RESULTS

The effects of DBZ on the development of atherosclerosis were studied using apolipoprotein E-deficient (apoE-/-) mice. For early treatment, 5-week-old apoE-/- mice were fed a Western diet and treated daily by oral gavage with or without DBZ or atorvastatin for 10 weeks. For advanced treatment, 5-week-old apoE-/- mice were fed a Western diet for 10 weeks to induce atherosclerosis, and then they were randomly divided into 4 groups and subjected to the treatment of vehicle, 20 mg/kg per day DBZ, 40 mg/kg per day DBZ, or 10 mg/kg per day atorvastatin for the subsequent 10 weeks. We showed that early treatment of apoE-/- mice with DBZ markedly reduced atherosclerotic lesion formation by inhibiting inflammation and decreasing macrophage infiltration into the vessel wall. Treatment with DBZ also attenuated the progression of preestablished diet-induced atherosclerotic plaques in apoE-/- mice. In addition, we showed that DBZ may affect LXR (liver X receptor) function and that treatment of macrophages with DBZ suppressed lipopolysaccharide-stimulated cell migration and oxidized low-density lipoprotein-induced foam cell formation.

CONCLUSIONS

DBZ potentially has antiatherosclerotic effects that involve the inhibition of inflammation, macrophage migration, leukocyte adhesion, and foam cell formation. These results suggest that DBZ may be used as a therapeutic agent for the prevention and treatment of atherosclerosis.

Bariatric surgery in morbidly obese patients improves the atherogenic qualitative properties of the plasma lipoproteins

OBJECTIVE

The purpose of this study was to evaluate the effect of weight loss induced in morbidly obese subjects by Roux-en-Y gastric bypass bariatric surgery on the atherogenic features of their plasma lipoproteins.

METHODS

Twenty-one morbidly obese subjects undergoing bariatric surgery were followed up for up to 1 year after surgery. Plasma and lipoproteins were assayed for chemical composition and lipoprotein-associated phospholipase A2 (Lp-PLA2) activity. Lipoprotein size was assessed by non-denaturing polyacrylamide gradient gel electrophoresis, and oxidised LDL by ELISA. Liver samples were assayed for mRNA abundance of oxidative markers.

RESULTS

Lipid profile analysis revealed a reduction in the plasma concentrations of cholesterol and triglycerides, which were mainly associated with a significant reduction in the plasma concentration of circulating apoB-containing lipoproteins rather than with changes in their relative chemical composition. All patients displayed a pattern A phenotype of LDL subfractions and a relative increase in the antiatherogenic plasma HDL-2 subfraction (>2-fold; P < 0.001). The switch towards predominantly larger HDL particles was due to an increase in their relative cholesteryl ester content. Excess weight loss also led to a significant decrease in the plasma concentration of oxidised LDL (∼-25%; P < 0.01) and in the total Lp-PLA2 activity. Interestingly, the decrease in plasma Lp-PLA2 was mainly attributed to a decrease in the apoB-containing lipoprotein-bound Lp-PLA2.

CONCLUSION

Our data indicate that the weight loss induced by bariatric surgery ameliorates the atherogenicity of plasma lipoproteins by reducing the apoB-containing Lp-PLA2 activity and oxidised LDL, as well as increasing the HDL-2 subfraction.

Functionally defective high-density lipoprotein and paraoxonase: a couple for endothelial dysfunction in atherosclerosis

The endothelium is the primary target for biochemical or mechanical injuries caused by the putative risk factors of atherosclerosis. Endothelial dysfunction represents the ultimate link between atherosclerotic risk factors that promote atherosclerosis. HDL-C is thought to exert at least some parts of its antiatherogenic facilities via stimulating endothelial NO production, nearby inhibiting oxidative stress and inflammation. HDL-C is capable of opposing LDL's inductive effects and avoiding the ox-LDL's inhibition of eNOS. Paraoxonase 1 (PON1) is an HDL-associated enzyme esterase which appears to contribute to the antioxidant and antiatherosclerotic capabilities of HDL-C. "Healthy HDL," namely the particle that contains the active Paraoxonase 1, has the power to suppress the formation of oxidized lipids. "Dysfunctional HDL," on the contrary, has reduced Paraoxonase 1 enzyme activity and not only fails in its mission but also potentially leads to greater formation of oxidized lipids/lipoproteins to cause endothelial dysfunction. The association of HDL-C PON1 and endothelial dysfunction depends largely on the molecules with exact damaging effect on NO synthase coupling. Loss of nitric oxide bioavailability has a pivotal role in endothelial dysfunction preceding the appearance of atherosclerosis. Analyses of HDL-C and Paraoxonase1 would be more important in the diagnosis and treatment of atherosclerosis in the very near future.

High Density Lipoprotein and it's Dysfunction

Plasma high-density lipoprotein cholesterol(HDL-C) levels do not predict functionality and composition of high-density lipoprotein(HDL). Traditionally, keeping levels of low-density lipoprotein cholesterol(LDL-C) down and HDL-C up have been the goal of patients to prevent atherosclerosis that can lead to coronary vascular disease(CVD). People think about the HDL present in their cholesterol test, but not about its functional capability. Up to 65% of cardiovascular death cannot be prevented by putative LDL-C lowering agents. It well explains the strong interest in HDL increasing strategies. However, recent studies have questioned the good in using drugs to increase level of HDL. While raising HDL is a theoretically attractive target, the optimal approach remains uncertain. The attention has turned to the quality, rather than the quantity, of HDL-C. An alternative to elevations in HDL involves strategies to enhance HDL functionality. The situation poses an opportunity for clinical chemists to take the lead in the development and validation of such biomarkers. The best known function of HDL is the capacity to promote cellular cholesterol efflux from peripheral cells and deliver cholesterol to the liver for excretion, thereby playing a key role in reverse cholesterol transport (RCT). The functions of HDL that have recently attracted attention include anti-inflammatory and anti-oxidant activities. High antioxidant and anti-inflammatory activities of HDL are associated with protection from CVD.This review addresses the current state of knowledge regarding assays of HDL functions and their relationship to CVD. HDL as a therapeutic target is the new frontier with huge potential for positive public health implications.

Emerging therapeutic strategies to enhance HDL function

Epidemiologic studies indicate a strong inverse correlation between plasma levels of high-density lipoproteins (HDL) and cardiovascular disease (CVD). The most relevant cardioprotective mechanism mediated by HDL is thought to be reverse cholesterol transport (RCT). New insights in HDL biology and RCT have allowed the development of promising agents aimed to increase HDL function and promote atherosclerosis regression. In this regard, apo-AI analogs and CETP inhibitors dalcetrapib and anacetrapib have aroused a great interest and opened new expectations in the treatment of CVD.