Inhibits ox-LDL Uptake Research Articles

Allogeneic Adipose-Derived Mesenchymal Stem Cell Transplantation Alleviates Atherosclerotic Plaque by Inhibiting Ox-LDL Uptake, Inflammatory Reaction and Endothelial Damage in Rabbits.

Atherosclerosis (AS) is a chronic inflammatory disease of arteries fueled by lipids. It is a major cause of cardiovascular morbidity and mortality. Mesenchymal stem cells have been used for the treatment of atherosclerotic lesions. Adipose-derived stem cells (ADSCs) have been shown to regulate the activation state of macrophages and exhibit anti-inflammatory capabilities. However, the effect of allogeneic ADSCs in the treatment of AS have not been investigated. In this study, the early treatment effect and preliminary mechanism analysis of allogeneic rabbit ADSCs intravenous transplantation were investigated in a high-fat diet rabbit model. The polarization mechanism of rabbit ADSCs on the macrophage was further analyzed in vitro. Compared with the model group, blood lipid levels declined, the plaque area, oxidized low-density lipoprotein (ox-LDL) uptake, scavenger receptor A1 and cluster of differentiation (CD) 36 levels were all significantly reduced, and the accumulation of inflammatory M1 macrophages, apoptosis, interleukin (IL)-6 and tumor necrosis factor (TNF)-α expression were decreased. The endothelial cells (CD31), M2 macrophages, IL-10 and the transforming growth factor (TGF)-β levels increased. In vitro, ADSCs can promote the M1 macrophage phenotypic switch toward the M2 macrophage through their secreted exosomes, and the main mechanism includes increasing arginase 1 expression and IL-10 secretion, declining inducible nitric oxide synthase (iNOS) expression and TNF-α secretion, and activating the STAT6 pathway. Therefore, allogeneic rabbit ADSC transplantation can transmigrate to the aortic atherosclerotic plaques and show a good effect in lowering blood lipids and alleviating atherosclerotic plaque in the early stage of AS by inhibiting ox-LDL uptake, inflammatory response, and endothelial damage.

Baicalein targets CD36 to prevent foam cell formation by suppressing the excessive uptake of oxLDL and accelerating ABCA1-mediated cholesterol efflux in oxLDL-induced THP-1 macrophages

• Baicalein can prevent oxLDL-induced foam cell formation in THP-1 macrophages. • Baicalein inhibits oxLDL uptake by preventing the binding of CD36 to oxLDL. • The binding of baicalein to CD36 triggers the Src-JNK-ABCA1 signalling pathway. • Baicalein enhances cholesterol efflux to avoid cholesterol accumulation. Oxidized low-density lipoprotein (oxLDL)-induced macrophage foam cell formation plays an important role in atherosclerosis progression. Baicalein is a constituent of Scutellaria baicalensis. Herein, we investigated the effect of baicalein on macrophage foam cell formation and the underlying mechanism. The THP-1 macrophage foam cell was established by oxLDL stimulation and the effects of baicalein on cholesterol uptake and efflux were analysed by molecular docking, ELISA, immunofluorescence, western blot, the inhibitor and siRNA experiment. The results showed that baicalein suppressed oxLDL-induced cholesterol accumulation. Mechanistically, baicalein reduced oxLDL uptake through competitive inhibiting the binding of CD36 to the epitope structure of oxLDL. Moreover, the binding of baicalein to CD36 enhanced the cholesterol efflux via the CD36-Src-JNK-ABCA1 signalling pathway. Meanwhile, Src and JNK inhibitors reversed the baicalein-induced reduction in cholesterol accumulation. In conclusion, these findings suggested that baicalein as a food supplement could inhibit macrophage foam cell formation and play an anti-atherosclerosis effect.

Gypenoside inhibits ox-LDL uptake and foam cell formation through enhancing Sirt1-FOXO1 mediated autophagy flux restoration

BackgroundGypenoside (GP) is the major bioactive constituent of G. pentaphyllum, a traditional Chinese medicine. It has been reported that GP can affect autophagy and lipid metabolism in cultured cells. We hypothesize that GP can inhibit foam cell formation in cultured macrophages through autophagy modulation. MethodsTHP1 cells were cultured and treated with oxidized low-density lipoprotein (ox-LDL), followed by GP treatment at different concentrations. The autophagy flux was evaluated using western blot and confocal microscope analyses. The ox-LDL uptake and foam cell formation abilities were measured. ResultsWe found that ox-LDL impaired the autophagy flux in the cultured macrophages, indicated by a significant reduction of LC3-II and autophagosome puncta quantification, as well as an accumulation of p62 proteins. GP treatment, however, dose-dependently restored the autophagy flux impaired by ox-LDL and reduced the ox-LDL uptake and foam cell transformation from THP1 cells, which can be alleviated, or exacerbated, by modulation of autophagy status using autophagy enhancer or inhibitor. Coimmunoprecipitation assays showed that GP up-regulated Srit1 and FOXO1 expression and enhanced their direct interaction, and thus contributed to the regulation of autophagy. ConclusionGP inhibits ox-LDL uptake and foam cell formation through enhancing Sirt1-FOXO1 mediated autophagy flux restoration, suggesting this compound has therapeutic potential for atherosclerosis.

Gly[14]-humanin inhibits ox-LDL uptake and stimulates cholesterol efflux in macrophage-derived foam cells

Foam cell formation, which is caused by imbalanced cholesterol influx and efflux by macrophages, plays a vital role in the occurrence and development of atherosclerosis. Humanin (HN), a mitochondria-derived peptide, can prevent the production of reactive oxygen species and death of human aortic endothelial cells exposed to oxidized low-density lipoprotein (ox-LDL) and has a protective effect on patients with in early atherosclerosis. However, the effects of HN on the regulation of cholesterol metabolism in RAW 264.7 macrophages are still unknown. This study was designed to investigate the role of [Gly14]-humanin (HNG) in lipid uptake and cholesterol efflux in RAW 264.7 macrophages. Flow cytometry and live cell imaging results showed that HNG reduced Dil-ox-LDL accumulation in the RAW 264.7 macrophages. A similar result was obtained for lipid accumulation by measuring cellular cholesterol content. Western blot analysis showed that ox-LDL treatment upregulated not only the protein expression of CD36 and LOX-1, which mediate ox-LDL endocytosis, but also ATP-binding cassette (ABC) transporter A1 and ABCG1, which mediate ox-LDL exflux. HNG pretreatment inhibited the upregulation of CD36 and LOX-1 levels, prompting the upregulation of ABCA1 and ABCG1 levels induced by ox-LDL. Therefore we concluded that HNG could inhibit ox-LDL-induced macrophage-derived foam cell formation, which occurs because of a decrease in lipid uptake and an increase in cholesterol efflux from macrophage cells.

Abstract 361: Oxidized Phospholipids Are Proinflammatory and Proatherogenic

Oxidized phospholipids (OxPL) are ubiquitously generated during inflammation, and found on apoptotic cells, OxLDL, and Lp(a). They facilitate uptake of OxLDL by macrophages (Mac) and mediate cellular inflammatory responses. The E06 natural IgM binds to the PC of OxPL, neutralizing biological effects and inhibiting OxLDL uptake by Mac. To determine the role of OxPL in atherogenesis, we generated transgenic mice expressing a single chain variant (scFv) of E06 in Ldlr background (E06-Tg). E06-scFv was secreted into plasma, bound to OxLDL and had sufficient titer to inhibit OxLDL uptake into Mac. E06-Tg or Ldlr mice were fed 1% Chol diet for 4, 7 or 12 months (n=12-15 mice/group). Plasma Chol was ~ 1600 mg/dL in all mice. Atherosclerosis decreased in E06-Tg mice: En face lesions decreased 57%, 34% and 28%, and aortic root lesions decreased 55%, 41% and 26% at 4, 7 and 12-months, respectively. OxLDL uptake by Macs was decreased: Thus, in E06-Tg mice, the uptake by peritoneal Mac of fluorescently-labeled OxLDL injected ip was decreased ~ 50%, as was peritoneal Mac Chol content. As Macs secrete E06-scFv, we performed BMT from E06-Tg donors into irradiated Ldlr recipients (n=10-12): This also decreased lesions 31% compared to BMT from control donors, even though plasma titers of E06-scFv were ~10% of Tg mice. Overexpression of E06-scFv was anti-inflammatory: Thus, in E06-Tg mice, both peritoneal and aortic wall resident macrophages exhibited decreased inflammatory gene expression, and phenotypic switches from M1 to M2 analyzed by RNAseq and FACS. Further, in E06-Tg mice, plasma SAA levels were reduced 32%, and hepatic steatosis was also decreased (-50% in both TG and Chol), as was hepatic inflammatory gene expression. Finally, E06-scFv attenuated both a progressive increase in aortic valve gradient (via echocardiography) and calcification in aged Ldlr mice. The E06-scFv lacks functional effects of an intact antibody other than the ability to “neutralize” OxPL. Thus, these data demonstrate that OxPL are profoundly proatherogenic and proinflammatory, which E06 counteracts in vivo . Neutralizing OxPL may therefore reduce the progression of atherosclerosis and cardiovascular events and more generally, represents a novel strategy to safely attenuate inflammation.

Protective role of n6/n3 PUFA supplementation with varying DHA/EPA ratios against atherosclerosis in mice

The effects of n3 polyunsaturated fatty acids (PUFA) on cardiovascular disease are controversial. We currently explored the effects of various ratios of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on high-fat-induced atherosclerosis. In model apoE−/− mice, high-fat diets (HFD) were partially replaced with fish and algal oils (DHA/EPA 2:1, 1:1 and 1:2) and/or plant oils enriched in linoleic and alpha-linolenic acids with an n6/n3 ratio of 4:1. PUFA supplementation significantly reduced the atherosclerotic plaque area, serum lipid profile, inflammatory response, aortic ROS production, proinflammatory factors and scavenger receptor expression as compared to those in the HFD group. However, plant oils did not have a significant effect on the following: serum HDL-C level; aortic ABCA1, ABCG1 and LAL mRNA expression; and CD36 and LOX-1 protein expression. Compared to the plant-oil-treated group, the DHA/EPA 1:1 group had a smaller atherosclerotic plaque area, higher serum HDL-C levels and lesser CD36 and MSR-1 mRNA expression; the DHA/EPA 2:1 group had lower serum TC, LDL-C and TNF-α levels and lower aortic ROS levels. Our study suggested that n3 PUFA from animals had more potent atheroprotective effects than that from plants. Supplementation involving higher DHA/EPA ratios and an n6/n3 ratio of 4:1 was beneficial for reducing serum “bad cholesterol” and a 1:1 DHA/EPA ratio with an n6/n3 ratio of 4:1 was beneficial for improving serum “good cholesterol” and inhibiting ox-LDL uptake. Our results suggest that achieving an n6/n3 ratio of 4:1 in the diet is also important in addition to having an optimal DHA/EPA ratio.

IL-10 negatively regulates oxLDL-P38 pathway inhibited macrophage emigration

The effect of IL-10 on macrophage migration was investigated, including the analysis of protein expression, cytokine secretion and activation of the MAPKs and NF-kB pathway. The expression of endogenic IL-10 was down-regulated in macrophage stimulated with oxLDL for indicated time. Exogenous IL-10 reversed oxLDL-inhibited chemotactic macrophage numbers by 48.18±4.93% (3h), 64.8±5.61% (6h) and 63.66±3.05% (12h), and pretreated with SB203580 (P38 signaling inhibitor) in macrophage, oxLDL could not inhibit macrophage emigration. IL-10 significantly decreased oxLDL-mediated increase of SR-A expression, and pretreatment with β-arrestin2 RNAi in macrophage could not change oxLDL-induced SR-A expression. IL-10 also significantly decreased oxLDL-mediated increase of β-arrestin2 expression, and pre-treated with SR-A RNAi in macrophage, oxLDL could not induce the increase of β-arrestin2 expression. However, IL-10 significantly reversed oxLDL-mediated inhibition of CCR7 expression about 95.78±0.99% (mRNA) and 80.06±19.46% (protein), and pretreated with P38 inhibitor SB203580 in macrophage, oxLDL could not decrease CCR7 expression. IL-10 inhibited oxLDL-mediated inhibition of MMP9 secretion about 74.02±22.35%, and pretreated with P38 inhibitor SB203580 in macrophage, oxLDL could not decrease MMP9 secretion. Treatment with oxLDL increased P38-phosphorylation by 31.88±2.79%, 40.24±5.69% and 30.93±4.66% at 15, 30 and 60min, respectively, whereas the effect of IL-10 on the expression of phosphorylated P38 was reversed by 49.49±12.12%, 70.93±16.14% and 47.62±6.00% in up-indicated time-points, respectively. From these data, we speculated oxLDL-SR-A-β-arrestin2-P38-MMP9/CCR7 could play a critical role in the macrophages migration, which was blocked by IL-10 through inhibiting oxLDL uptake.

GLP-1 Agonists Inhibit ox-LDL Uptake in Macrophages by Activating Protein Kinase A

Oxidized low-density lipoprotein (ox-LDL) uptake by monocytes/macrophages plays a pivotal role in atherogenesis. This study was designed to examine the effect of glucagon-like peptide-1 (GLP-1) agonists on ox-LDL uptake in macrophages. Human primary monocytes/macrophages were incubated with native GLP-1 (nGLP-1) or GLP-1 agonist liraglutide to evaluate their effect on ox-LDL uptake and the expression of scavenger receptors (SRs), such as SR-A, CD36, and lectin-like ox-LDL SR-1, in this process. Our study showed a decrease in ox-LDL uptake and CD36 expression in macrophages treated with nGLP-1 or liraglutide. However, nGLP-1 and liraglutide did not affect the expression of other SRs SR-A and lectin-like ox-LDL SR-1. Simultaneously, there was an increase in the expression of activated protein kinase A (PKA). To examine the role of PKA in the effects of nGLP-1 or liraglutide, we treated macrophages with PK inhibitor (6-22) amide, a PKA inhibitor, followed by treatment with nGLP-1 or liraglutide. Inhibition of PKA activation markedly reversed the effect of nGLP-1 or liraglutide on ox-LDL uptake and enhanced the expression of CD36. Our results suggest that GLP-1 agonism inhibits ox-LDL uptake through PKA/CD36 pathway in macrophages. This study provides a novel insight in the mechanism of foam cell formation and the role by GLP-1 agonists therein.

Tanshinone IIA suppresses cholesterol accumulation in human macrophages: role of heme oxygenase-1

Accumulation of foam cells in the neointima represents a key event in atherosclerosis. We previously demonstrated that Tanshinone IIA (Tan), a lipophilic bioactive compound extracted from Salvia miltiorrhiza Bunge, inhibits experimental atherogenesis, yet the detailed mechanisms are not fully understood. In this study, we sought to explore the potential effects of Tan on lipid accumulation in macrophage foam cells and the underlying molecular mechanisms. Our data indicate that Tan treatment reduced the content of macrophages, cholesterol accumulation, and the development of atherosclerotic plaque in apolipoprotein E-deficient mice. In human macrophages, Tan ameliorated oxidized low density lipoporotein (oxLDL)-elicited foam cell formation by inhibiting oxLDL uptake and promoting cholesterol efflux. Mechanistically, Tan markedly reduced the expression of scavenger receptor class A and increased the expression of ATP-binding cassette transporter A1 (ABCA1) and ABCG1 in lipid-laden macrophages via activation of the extracellular signal-regulated kinase (ERK)/nuclear factor-erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway. Tan treatment induced the phosphorylation and nuclear translocation of Nrf2 and subsequently increased the expression of HO-1, and these effects were abolished by the specific ERK inhibitors, PD98059 and U0126. Moreover, HO-1 small interfering RNA or zinc protoporphyrin (a HO-1 inhibitor) abrogated Tan-mediated suppression of lipid accumulation in macrophages. Our current findings demonstrate that a novel HO-1-dependent mechanism is involved in the regulation of cholesterol balance by Tan.

Simvastatin increases Prolyl-4-Hydroxylase α1 expression in atherosclerotic plaque and ox-LDL-stimulated human aortic smooth muscle cells via p38 MAPK and ERK1/2 signaling

Prolyl-4-Hydroxylase α1 (P4Hα1) is essential for collagen synthesis but the effect of statin on P4Hα1 is unknown. We hypothesize that simvastatin may increase the expression of P4Hα1 in atherosclerotic plaques and ox-LDL-stimulated human aortic smooth muscle cells (HASMCs). In HASMCs, ox-LDL suppressed P4Hα1 expression significantly with peak value occurring at 50ug/ml treated for 8h. Ox-LDL also inhibited the expression of type I and III collagen and increased the phosphorylation level of p38 MAPK and ERK1/2, but blockade or silencing of p38 and ERK1/2 inhibited the suppressive effect of ox-LDL on P4Hα1. Then HASMCs were stimulated with or without ox-LDL (50ug/ml) for 8h after simvastatin pretreatment for 1h. Simvastatin significantly attenuated the suppressive effect of ox-LDL on P4Hα1 and collagen production by inhibiting ox-LDL uptake and the activation of p38 MAPK and ERK1/2. In apolipoprotein E-deficient mice, simvastatin and the inhibitors of p38 and ERK1/2 significantly increased the stability of the carotid plaques. We also found that simvastatin significantly increased the expression of P4Hα1 and collagen possibly due to decreased ox-LDL content and phosphorylation of p38 and ERK1/2 in plaques. Thus, simvastatin increases P4Hα1 and collagen expression in ox-LDL-stimulated HASMCs and atherosclerotic plaques via p38 MAPK and ERK1/2, thereby exerting a plaque stabilizing effect.

Vitamin E reduces the uptake of oxidized LDL by inhibiting CD36 scavenger receptor expression in cultured aortic smooth muscle cells.

Vitamin E is well known as an antioxidant, and numerous studies suggest that it has a preventive role in atherosclerosis, although the mechanism of action still remains unclear. The original aim of this study was to establish whether alpha-tocopherol (the most active form of vitamin E) acts at the earliest events on the cascade of atherosclerosis progression, that of oxidized LDL (oxLDL) uptake and foam-cell formation. We show here that the CD36 scavenger receptor (a specific receptor for oxLDL) is expressed in cultured human aortic smooth muscle cells (SMCs). Treatment of SMCs and HL-60 macrophages with alpha-tocopherol (50 micromol/L, a physiological concentration) downregulates CD36 expression by reducing its promoter activity. Furthermore, we find that alpha-tocopherol treatment of SMCs leads to a reduction of oxLDL uptake. This study indicates that CD36 is expressed in cultured human SMCs. In these cells, CD36 transports oxLDL into the cytosol. alpha-Tocopherol inhibits oxLDL uptake by a mechanism involving downregulation of CD36 mRNA and protein expression. Therefore, the beneficial effect of alpha-tocopherol against atherosclerosis can be explained, at least in part, by its effect of lowering the uptake of oxidized lipoproteins, with consequent reduction of foam cell formation.