Scholarly article on topic 'Foam cells in atherosclerosis'

Foam cells in atherosclerosis Academic research paper on "Basic medicine"

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Clinica Chimica Acta
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{"Foam cells" / Atherosclerosis / CD36 / ACAT1 / ABCA1 / ABCG1}

Abstract of research paper on Basic medicine, author of scientific article — Xiao-Hua Yu, Yu-Chang Fu, Da-Wei Zhang, Kai Yin, Chao-Ke Tang

Abstract Atherosclerosis is a chronic disease characterized by the deposition of excessive cholesterol in the arterial intima. Macrophage foam cells play a critical role in the occurrence and development of atherosclerosis. The generation of these cells is associated with imbalance of cholesterol influx, esterification and efflux. CD36 and scavenger receptor class A (SR-A) are mainly responsible for uptake of lipoprotein-derived cholesterol by macrophages. Acyl coenzyme A:cholesterol acyltransferase-1 (ACAT1) and neutral cholesteryl ester hydrolase (nCEH) regulate cholesterol esterification. ATP-binding cassette transporters A1(ABCA1), ABCG1 and scavenger receptor BI (SR-BI) play crucial roles in macrophage cholesterol export. When inflow and esterification of cholesterol increase and/or its outflow decrease, the macrophages are ultimately transformed into lipid-laden foam cells, the prototypical cells in the atherosclerotic plaque. The aim of this review is to describe what is known about the mechanisms of cholesterol uptake, esterification and release in macrophages. An increased understanding of the process of macrophage foam cell formation will help to develop novel therapeutic interventions for atherosclerosis.

Academic research paper on topic "Foam cells in atherosclerosis"


CCA-13117; No of Pages 8

Clinica Chimica Acta xxx (2013) xxx-xxx

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Clinica Chimica Acta

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Invited critical review

Foam cells in atherosclerosis^

Xiao-hua Yu a, Yu-chang Fuc, Da-Wei Zhang d, Kai Yin Chao-ke Tang a'b'**

a Life Science Research Center, University of South China, Hengyang, Hunan 421001, China

b Institute of Cardiovascular Research, Key Laboratory for Atherosclerology of Hunan Province, University of South China, Hengyang, Hunan 421001, China c Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL 35294-0012, USA

d Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta T6G 2S2, Canada

article info


Article history:

Received 25 April 2013

Received in revised form 4 June 2013

Accepted 6 June 2013

Available online xxxx



Foam cells

Atherosclerosis is a chronic disease characterized by the deposition of excessive cholesterol in the arterial intima. 28 Macrophage foam cells play a critical role in the occurrence and development of atherosclerosis. The generation of 29 these cells is associated with imbalance of cholesterol influx, esterification and efflux. CD36 and scavenger receptor 30 class A (SR-A) are mainly responsible for uptake of lipoprotein-derived cholesterol by macrophages. Acyl coen- 31 zyme A:cholesterol acyltransferase-1 (ACAT1) and neutral cholesteryl ester hydrolase (nCEH) regulate cholesterol 32 esterification. ATP-binding cassette transporters A1(ABCA1),ABCG1 and scavenger receptor BI (SR-BI) play crucial 33 roles in macrophage cholesterol export. When inflow and esterification of cholesterol increase and/or its outflow 34 decrease, the macrophages are ultimately transformed into lipid-laden foam cells, the prototypical cells in the 35 atherosclerotic plaque. The aim of this review is to describe what is known about the mechanisms of cholesterol 36 uptake, esterification and release in macrophages. An increased understanding of the process of macrophage 37 foam cell formation will help to develop novel therapeutic interventions for atherosclerosis. 38

© 2013 The Authors. Published by Elsevier B.V. All rights reserved. 39


1. Introduction .............................................................. 0

2. Cholesterol uptake ........................................................... 0

2.1. CD36 .............................................................. 0

2.2. SR-A............................................................... 0

3. Cholesterol esterification......................................................... 0

3.1. ACAT1.............................................................. 0

3.2. nCEH .............................................................. 0

4. Cholesterol efflux............................................................ 0

4.1. ABCA1.............................................................. 0

4.2. ABCG1.............................................................. 0

4.3. SR-BI .............................................................. 0

5. Conclusion and future directions..................................................... 0

Acknowledgment............................................................... 0

References.................................................................. 0

Abbreviations: ABCA1, ATP-binding cassette transporter A1; ABCG1, ATP-binding cassette transporter G1; SR-BI, scavenger receptor BI; SR-A, scavenger receptor class A; ACAT1, acyl coenzyme A:cholesterol acyltransferase-1; nCEH, neutral cholesteryl ester hydrolase; ox-LDL, oxidized low-density lipoprotein; HDL, high-density lipoprotein; apoA-I, apolipoprotein A-I; LDLR, low-density lipoprotein receptor; apoE, apolipoprotein E; CE, cholesterol ester; FC, free cholesterol; LXR, liver X receptor; RXR retinoid X receptor; PPAR-y, peroxisome proliferator-activated receptor-y; ERK1/2, extracellular signal-regulated kinases 1 and 2; PPREs, PPAR response elements; PKB, protein kinase B; PKC, protein kinase C; TGF-p, transforming growth factor-p; MAPK, mitogen-activated protein kinase; RCT, reverse cholesterol transport; PI3K, phosphatidylinositol 3-kinase; AGE, advanced glycation end products. ☆ This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Corresponding author. Tel./fax: +86 734 8281852.

** Correspondence to: Institute of Cardiovascular Research, University of South China, Hengyang, Hunan 421001, China. Tel./fax: +86 734 8281853. E-mail addresses: (K. Yin), (C. Tang).

0009-8981/$ - see front matter © 2013 The Authors. Published by Elsevier B.V. All rights reserved.! 0.1016/j.cca.2013.06.006


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx

1. Introduction

Atherosclerotic diseases are the major causes of mortality and morbidity in the world. Formation of macrophage foam cells in the intima is a major hallmark of early stage atherosclerotic lesions. Uncontrolled uptake of oxidized low-density lipoprotein (ox-LDL), excessive cholesterol esterification and/or impaired cholesterol release result in accumulation of cholesterol ester (CE) stored as cytoplasmic lipid droplets and subsequently trigger the formation of foam cells. Scavenger receptors (SRs), CD36 and SR class A (SR-A) are the principal receptors responsible for the binding and uptake of ox-LDL in macrophages [1]. Acyl coenzyme A:cholesterol acyltransferase-1 (ACAT1) and neutral cholesteryl ester hydrolase (nCEH) play a critical role in cholesterol esterification [2]. ATP-binding cassette (ABC) transporter A1(ABCA1), ABCG1 and scavenger receptor-B[ (SR-BI) mediate cholesterol export from macrophages [3]. This review focuses on the recent developments in our knowledge of the roles and regulation of these receptors, enzymes and transporters in the formation of macrophage foam cells.

2. Cholesterol uptake

Cholesterol uptake is a pathway by which extracellular modified LDL are ingested by macrophages via receptors-mediated phagocytosis and pinocytosis. SRs such as SR-A and CD36 have been implicated in this process. In vitro studies have shown that CD36 and SR-A account for 75% to 90% of ox-LDL internalization by macrophages, whereas other SRs cannot compensate for their absence [4]. Thus, CD36 and SR-A are the most important receptors responsible for the uptake of modified lipoproteins by macrophages.

2.1. CD36

CD36 is first identified as the platelet glycoprotein III b/IV, an 88 kDa heavily glycosylated transmembrane protein that belongs to SR class B family. It consists of an extracellular domain flanked by two transmembrane and two cytoplasmic domains. CD36 functions

as a high-affinity receptor for ox-LDL. A domain located between 93 amino acids 155 and 183 of CD36 involves in ox-LDL binding. Other 94 ox-LDL binding sites have also been reported such as amino acids 95 28-93 and possibly 120-155. Binding of ox-LDL to CD36 leads to 96 endocytosis through a lipid raft pathway that is distinct from the 97 clathrin-mediated or caveolin internalization pathways. The patho- 98 genic role of ox-LDL in atherosclerosis largely depends on CD36. A 99 recent study revealed that plasma soluble CD36 correlates significant- 100 ly with markers of atherosclerosis, insulin resistance and fatty liver in 101 a nondiabetic healthy population [5]. Patients with acute coronary 102 syndromes exhibit a significant increase in CD36 expression in circu- 103 lating monocytes, which can be inhibited by a 6-month treatment of 104 atorvastatin [6]. Small molecules with anti-CD36 activity have been 105 shown to decrease postprandial hyperlipidemia and protect against 106 atherosclerosis [7]. In addition, the 573A allele of CD36 has a protec- 107 tive effect against atherosclerosis development while the 591T allele 108 is a cardiovascular risk factor [8]. On the other hand, Moore and col- 109 leagues reported that apoE-/- mice lacking CD36 or SR-A display in- 110 creased aortic sinus atherosclerotic lesion area and abundant 111 macrophage foam cells in the aortic intima despite reductions in peri- 112 toneal macrophage CE accumulation in vivo [9]. Moreover, clinical 113 studies show that patients with CD36 deficiency are associated with 114 severe and enhanced atherosclerotic diseases [10]. Therefore, the 115 role of CD36 as a proatherogenic mediator of ox-LDL uptake in vivo 116 needs to be reassessed. 117

CD36 is highly expressed in macrophages and its expression is regu- 118 lated by multiple factors (Fig. 1). Recently, Inoue et al. reported that 119 astaxanthin (ASX), an oxygenated carotenoid (xanthophyll), signifi- 120 cantly increases CD36 levels in peritoneal macrophages by stimulating 121 peroxisome proliferator-activated receptor-Y (PPARy) [11]. On the 122 other hand, curcumin, a potent antioxidant extracted from Curcuma 123 longa, induces a PPARY-independent CD36 overexpression through 124 upregulating nuclear erythroid-related factor 2(Nrf2) [12]. Additionally, 125 Gao et al. reported that palmitate increases CD36 expression in mono- 126 cytes through the regulation of de novo ceramide synthesis [13]. Sup- 127 plementation of the mushroom Agaricus blazei for 12 weeks markedly 128 elevates CD36 expression and plaque vulnerability in apoE-/- mice, 129



e^o t№q 1 1 1 11

Kaempferol Palmitate fTSIIA ASX

JSqualene Walnut

I i I I I


Fig. 1. Regulation of CD36 and SR-A expression in macrophages. CD36 expression is induced by ASX and inhibited by TSIIA and quercitrin via PPARy pathway. Palmitate increases CD36 levels while kaempferol, EM-1, squalene and walnut reduce its levels. Curcumin also upregulates CD36 expression through promoting Nrf-2 nuclear translocation but decreases SR-A protein expression via UPS. Berberine, Kv1.3 and TNF-a enhance SR-A levels, whereas MLPE and H2S diminish its levels. RXR: retinoid X receptor.


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx 3

130 indicating a proatherogenic property of mushroom A. blazei [14]. In

131 contrast, a dietary compound quercitrin inhibits CD36 expression in

132 murine macrophages through interfering with PKC/PPARy signaling

133 cascades [15]. Tanshinone IIA (TSIIA), a lipophilic diterpene isolated

134 from Salvia miltiorrhiza Bunge (Danshen), also decreases CD36 levels

135 in ox-LDL treated macrophages by antagonism of PPARy [16]. Similarly,

136 endomorphin-1(EM-1), a member of the endogenous opioid peptides

137 family, and squalene, one of the components of olive oil, downregulate

138 CD36 expression and prevent lipid accumulation in human lipid-laden

139 macrophages [17,18]. Treatment of macrophages with kaempferol

140 inhibits c-Jun/activator protein-1 (AP-1) nuclear translocation and

141 leads to the downregulation ofCD36 expression [19]. Atheroprotective

142 effect of dietary intake of walnut that enriches in n-3 polyunsaturated

143 fatty acids and antioxidant compounds, is associated with reduced

144 CD36 expression in apoE-/- mice [20]. In addition, the combined treat-

145 ment of interferon y and tumor necrosis factor a (TNF-a) significantly

146 reduces CD36 levels [21]. Thus, these factors may act as novel modula-

147 tors for macrophage-to-foam cell transformation.

3. Cholesterol esterification 193

In addition to cholesterol uptake, the balance of free cholesterol 194 (FC) and CE is also critical for the regulation of intracellular cholester- 195 ol content in macrophage foam cells. After internalization, lipopro- 196 teins are delivered to the late endosome/lysosome, where CE is 197 hydrolyzed into FC by lysosomal acid lipase (LAL). To prevent the 198 FC-associated cell toxicity, the FC released is re-esterified on the en- 199 doplasmic reticulum (ER) by ACAT1 and stored in cytoplasmic lipid 200 droplets. If this persistently occurs, excessive CE will accumulate in 201 macrophages, thereby resulting in the formation of foam cells. 202 These cells are often referred to as foam cells because of their charac- 203 teristic "foamy" appearance. The resulting CE are hydrolyzed by nCEH 204 to release FC for transporters-mediated efflux, which is increasingly 205 being recognized as the rate-limiting step in FC outflow [31]. Thus, 206 the cycle of esterification and hydrolysis of CE is one of the key 207 steps in maintaining intracellular cholesterol homeostasis, and 208 ACAT1 and nCEH play a crucial role in the process. 209

148 2.2. SR-A

149 SR-A, a 77-kDa cell surface glycoprotein, is a member of class A SR

150 family. The human and murine SR-A genes are located on chromo-

151 some 8 and can be transcribed to produce three (SR-AI/II/III) and

152 two SR-A splice variants, respectively. SR-A is highly expressed in

153 macrophages and mediates the uptake of ox-LDL into macrophages.

154 Inhibition of SR-A in macrophages significantly ameliorates foam

155 cell formation and atherosclerosis in apoE-/- mice [22]. Silencing

156 of SR-A or CD36 alone reduces atherogenesis in LDL receptor

157 (LDLR)-deficient apolipoprotein B100 mice, whereas simultaneous

158 silencing of both receptors has no beneficial effect, suggesting that

159 the compensatory upregulation of the two receptors is sufficient for

160 the uptake of modified LDL [23]. Conversely, completely knockout of

161 SR-A alone aggravates atherosclerosis despite of reduced peritoneal

162 macrophage lipid accumulation [9], but combined deletion of SR-A

163 and CD36 reduces atherosclerotic lesion complexity without affecting

164 foam cell formation in hyperlipidemic mice, indicating that specific

165 inhibition of these pathways in vivo may promote plaque stability

166 [24]. Thus, further studies are necessary to clarify the role of SR-A in

167 atherosclerosis.

168 The expression level of SR-A is upregulated by a variety of agents

169 (Fig. 1). Treatment of ox-LDL stimulates SR-A expression and pro-

170 motes the uptake of ox-LDL into macrophages. Li and colleagues

171 reported that berberine significantly elevates mRNA and protein

172 levels of SR-A in mouse RAW264.7 cells through inhibiting PTEN ex-

173 pression and sustaining Akt activation [25]. Proinflammatory cyto-

174 kines such as TNF-a also induce SR-A expression but via

175 suppression of nuclear factor-KB (NF-kB) signaling [26]. More recent-

176 ly, voltage-gated potassium channel Kv1.3 has been shown to

177 upregulate SR-A expression in human monocyte-derived macro-

178 phages, revealing that specific Kv1.3 blockade may represent a

179 novel strategy to modulate cholesterol metabolism in macrophages

180 [27]. Taken together, these findings indicate that inhibition of these

181 agents may reduce the uptake of ox-LDL by macrophages and then

182 prevent the formation of foam cells.

183 Hydrogen sulfide (H2S), curcumin and mulberry leaf polyphenolic

184 extracts (MLPE) have been reported to decrease SR-A expression

185 (Fig. 1). Our previous studies have shown that H2S reduces SR-A ex-

186 pression and foam cell formation in human monocyte-derived macro-

187 phages via the K(ATP)/ERK1/2 pathway [28]. Curcumin decreases

188 SR-A protein levels in macrophages through the ubiquitin/proteasome

189 system(UPS)-dependent proteolysis [29]. On the other hand, MLPE

190 inhibits PPARy and then reduces macrophage SR-A levels, suggesting

191 a protective role of MLPE in regulating intracellular lipid homeostasis

192 within the intima [30].

3.1.ACAT1 210

ACAT1 is an integral membrane protein that converts FC into the 211 storage form of CE. It has already been reported that ACAT1 deficiency 212 increases the synthesis and efflux of FC in mouse peritoneal macro- 213 phages while its overexpression promotes CE accumulation and 214 macrophage-derived foam cell formation [32,33]. However, the role 215 of ACAT1 in atherosclerosis is currently under debate. Kusunoki et 216 al. revealed that ACAT1 inhibition attenuates atherosclerosis in apoE 217 mice [34]. On the other hand, mice lacking macrophage-derived 218 ACAT1 show accelerated atherosclerosis [35,36]. This may be due to 219 the cytotoxic effects of increased FC levels, which crystallize in mac- 220 rophage foam cells. The formation of cholesterol crystals not only 221 destroys cholesterol metabolism during the development of athero- 222 sclerosis, but also facilitates the secretion of inflammatory mediators 223 such as IL-1p and IL-18 [37]. Taken together, the effects of ACAT1 on 224 atherosclerosis remain to be further investigated. 225

Numerous steps have been implicated in the modulation of ACAT1 226 expression (Fig. 2). Insulin has been shown to enhance ACAT1 expres- 227 sion in THP-1 macrophages via MAP kinases (MAPK)/CCAAT/enhanc- 228 er binding protein a(C/EBPa) signaling pathway [38]. Yang et al. 229 observed that voltage-gated potassium channel Kv1.3 significantly 230 upregulates ACAT1 expression and increases percentage of CE in 231 human monocyte-derived macrophages exposed to ox-LDL [27]. 232 Chlamydia pneumoniae (C. pneumoniae) infection is reported to in- 233 crease ACAT1 expression and disturb cholesterol homeostasis 234 through c-Jun NH(2) terminal kinase (JNK)/PPARy dependent signal 235 transduction pathways [39]. Leptin, an adipose tissue-derived hor- 236 mone, accelerates CE accumulation in human monocyte-derived mac- 237 rophages by increasing ACAT1 expression via Janus-activated kinase 2 238 (JAK2) and PI3K [40]. In contrast, treatment of cultured THP-1 macro- 239 phages in vitro with an angiotensin receptor blocker, candesartan, 240 leads to a decrease in ACAT1 expression [41]. Incretins such as 241 glucagon-like peptide-1 (GLP-1) and glucose-dependent insulino- 242 tropic polypeptide (GIP) are also able to decrease the levels of 243 ACAT1 by cAMP activation [42]. Our recent studies showed that H2S 244 inhibits macrophage foam cell formation by suppressing ACAT1 ex- 245 pression via K(ATP)/ERK1/2 pathway [28]. Additionally, ghrelin, an 246 endogenous ligand of the growth hormone secretagogue receptor 247 (GHS-R), lowers the expression of ACAT1 in THP-1 macrophages via 248 pathways involving GHS-R and PPARy, indicating a protective role 249 for ghrelin in controlling cellular lipid accumulation [43]. 250

3.2. nCEH 251

The esterification of FC into CE by ACAT1 is opposed by nCEH, 252 which hydrolyzes CE to cholesterol for efflux out of the cells. nCEH 253


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx Candesartan C. pneumoniae Ghrelin

Fig. 2. Regulation of ACAT1 and nCEH expression in macrophages. ACAT1 is upregulated by insulin, Kv1.3, C. pneumoniae and leptin but downregulated by candesartan, GLP-1, GIP, H2S and ghrelin. PUFA increases nCEH expression while insulin and IL-33 decrease its expression.

is a single-membrane-spanning type II membrane protein including three domains: N-terminal, catalytic, and lipid-binding domains. The N-terminal domain acts as a type II signal anchor sequence to recruit nCEH to the ER with its catalytic domain within the lumen [44]. N-linked glycosylation at Asn270 is important for its enzymatic activity. One recent study by Igarashi et al. showed that overexpression of human nCEH promotes the hydrolysis of CE and thereby stimulates cholesterol mobilization from THP-1 macrophages while knockdown of nCEH markedly accelerates the formation of foam cells, further conforming the key role for nCEH in maintaining intra-cellular cholesterol equilibrium [45]. Moreover, genetic ablation of nCEH also facilitates the development of atherosclerosis in apoE-/-mice without affecting their serum lipid profile [46]. Conversely, macrophage-specific overexpression of nCEH leads to a significant reduction in atherosclerotic lesion area in LDLR-/- mice because of enhanced FC efflux and reverse cholesterol transport (RCT) [47]. Overall, these results demonstrate the antiatherogenic role of nCEH and indicate that this enzyme is a promising target for the treatment of atherosclerosis.

nCEH is robustly expressed in macrophages as well as in atherosclerotic lesions. Polyunsaturated fatty acid (PUFA), insulin and IL-33 have been described to modulate its expression (Fig. 2). Napolitano and colleagues have reported that PUFA derived from corn oil can induce nCEH expression in J774 macrophages [48]. On the other hand, insulin significantly suppresses the expression of nCEH in THP-1 macrophages, partially accounting for the potential molecular mechanism of atherogenesis in type 2 diabetes with hyperinsulinemia [49]. IL-33, a recently discovered member of the 1L-1 cytokine family, also reduces nCEH mRNA levels in primary human monocyte-derived macrophages by activating ST-2/NF-kB signaling pathway [50,51]. Variety of other factors that can regulate nCEH expression will be probably found in later researches.

4. Cholesterol efflux

The first step of RCT is cholesterol efflux, namely, accumulated cholesterol is removed from macrophages in the subintima of the vessel wall through transporters or other mechanisms such as passive diffusion, and then collected by high-density lipoprotein (HDL) or

apolipoprotein A-I (apoA-1). Active transport via transporters includ- 291

ing the best characterized ABCA1, ABCG1 and SR-BI is mainly respon- 292

sible for the bulk efflux of cholesterol from macrophages onto 293

extracellular acceptors. 294

4.1.ABCA1 295

ABCA1 is a member of the large superfamily of ABC transporters. It is 296

now well established that ABCA1 plays a critical role in the prevention 297

of macrophage foam cell formation and atherosclerosis by mediating 298

the active transport of intracellular cholesterol and phospholipids to 299

apoA-1, the major lipoprotein in HDL. Bochem and colleagues have dem- 300

onstrated that ABCA1 mutation carriers show lower HDL-cholesterol 301

(HDL-C) levels and a larger atherosclerotic burden compared with con- 302

trols [52]. Unexpectedly, mice lacking ABCA1 and SR-BI display severe 303

hypocholesterolemia and foam cell accumulation, but have no athero- 304

sclerosis, which is mainly due to the absence of proatherogenic lipopro- 305

teins [53]. ABCA1 overexpression in the liver of LDLR-/- mice results in 306

accumulation of proatherogenic lipoproteins and enhanced atheroscle- 307

rosis [54]. Thus, in regard to these contradictory observations, a careful 308

re-evaluation of ABCA1 as a potent antiatherogenic agent is necessary. 309

The expression of ABCA1 is highly regulated by multiple processes 310 (Fig. 3). Lee et al. observed that quercetin stimulates PPAR^/liver X 311

receptor a (LXRa) signaling and then increases ABCA1 expression 312

and cholesterol efflux from THP-1 macrophages, indicating that in- 313 gestion of quercetin or quercetin-rich foods may be an effective way 314 to lower the risks of atherosclerosis [55]. Studies from our laboratory 315

showed that apelin-13, a recently discovered adipocytokine, en- 316

hances ABCA1 expression in THP-1 macrophage-derived foam cells 317

via activating the PKCa pathway and inhibiting calpain activity [56]. 318

Toll-like receptor 2 (TLR2) agonist Pam(3)CSK(4) raises ABCA1 levels 319

in RAW 264.7 macrophages via activation of PKC-n/phospholipase D2 320 (PLD2) signaling pathway [57]. S-allylcysteine, the most abundant 321

organosulfur compound in aged garlic extract, also elevates ABCA1 322

content in human THP-1 macrophages [58]. On the other hand, unsat- 323

urated fatty acids suppress ABCA1 expression in RAW 264.7 macro- 324

phages by two distinct mechanisms: LXR-dependent transcriptional 325

repression possibly through modulating histone acetylation states, 326

and LXR-independent posttranslational inhibition [59]. Our previous 327


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx

Apelin-13 1 l P3m(3)CSK(4)

Fig. 3. Regulation of ABCA1, ABCG1 and SR-BI expression in macrophages. ABCA1 expression is induced by apelin-13, Pam(3)CSK(4) and quercetin but inhibited by miR-26 and IL-18 plus IL-12. Cineole, EVOO and fucosterol upregulate ABCG1 expression by activating LXR whereas LPS downregulates its expression. In addition, PCA increases ABCG1 levels via suppression of miR-10b. Res, LA, hydrogen and coffee lead to a significant elevation in the SR-BI levels while PAPP-A treatment reduces its levels. P: phosphorylation, APJ: G-protein coupled receptor.

328 studies indicate that IL-18 and IL-12 synergistically decrease ABCA1

329 levels in THP-1 macrophage-derived foam cells through the IL-18 re-

330 ceptor (IL-18R)/NF-KB/zinc finger protein 202 (ZNF202) signaling

331 pathway [60]. In addition, miR-26 prevents ABCA1 expression and

332 subsequent cholesterol efflux from macrophages to apoA-I via

333 targeting LXRa, indicating a novel regulatory role of miR-26 in cellu-

334 lar lipid accumulation within the intima [61]. Thus, miR-26 inhibitors

335 can be potentially used to treat atherosclerosis.

336 4.2. ABCG1

[69]. Protocatechuic acid (PCA), a gut microbiota metabolite of 361 cyanidin-3 to 0-(3-glucoside, exerts an antiatherogenic effect partially 362 through inhibition of miR-10b-mediated downregulation of ABCG1 ex- 363 pression, indicating that gut microbiota is a potential novel target for pre- 364 vention and treatment of atherosclerosis [70]. Conversely, subclinical 365 low-dose lipopolysaccharide (LPS) potently reduces the expression of 366 ABCG1 in bone marrow-derived macrophages through interleukin-1 367 receptor-associated kinase 1(IRAK-1)/glycogen synthase kinase 3(3 368 (GSK3()/retinoic acid receptor a (RARa) signaling pathway, revealing 369 a novel intracellular network regulated by low-dose endotoxemia [71]. 370

337 ABCG1 mediates cholesterol removal from macrophages to HDL

338 particles but not to lipid-free apoA-I. It has been shown that a func-

339 tional genetic variant in the ABCG1 promoter is associated with an

340 increased risk of myocardial infarction and ischemic heart disease in

341 the general population [62]. Lack of macrophage ABCG1 has been

342 reported to cause a modest increase in atherosclerotic lesions [63].

343 However, two other independent groups reported that LDLR-/-

344 mice lacking macrophage ABCG1 show decreased atherosclerotic

345 lesions [64,65]. Most recently, Meurs and colleagues found that the

346 absence of ABCG1 leads to increased lesions in early stage of athero-

347 sclerosis but causes retarded lesion progression in more advanced

348 stage of atherosclerosis in LDLR-/- mice, suggesting that the influ-

349 ence of ABCG1 deficiency on lesion development depends on the

350 stage of atherogenesis [66]. Therefore, the impact of ABCG1 on the

351 development of atherosclerosis is complex and needs to be further

352 investigated.

353 The regulation of ABCG1 expression has similarities with that of

354 ABCA1, consistent with a shared role in cholesterol export (Fig. 3).

355 Cineole, a small aroma compound in teas and herbs, induces ABCG1 ex-

356 pression in macrophages through the activation of LXR [67]. Fucosterol,

357 a sterol that is abundant in marine algae, is also able to increase ABCG1

358 levels in a LXR-dependent mechanism [68]. Consumption of extra-

359 virgin olive oil (EVOO) for 12 weeks induces a concentration-

360 dependent upregulation of ABCG1 expression in human macrophages

4.3. SR-BI 371

SR-BI promotes cholesterol efflux from macrophages to HDL. A 372 genetic variant of the SR-BI in humans leads to a reduction in choles- 373 terol efflux from macrophages but has no significant increase in ath- 374 erosclerosis [72]. On the other hand, inactivation of macrophage 375 SR-BI facilitates atherosclerotic lesion development in apoE-/- mice 376

[73]. However, a recent report suggests that the presence of macro- 377 phage SR-BI inhibits advanced atherosclerotic lesion but promotes 378 early lesion development in LDLR-/- mice, indicating a unique dual 379 role for macrophage SR-BI in the pathogenesis of atherosclerosis 380

[74]. SR-BI is also highly expressed in the liver. Hepatic SR-BI expres- 381 sion is a positive regulator of the rate of RCT from macrophages to the 382 liver, bile, and feces. Of note, inhibition of hepatic SR-BI using RNA in- 383 terference technique reduces atherosclerosis in rabbits fed with 384 cholesterol-rich diet, indicating that the effect of SR-BI on atherogen- 385 esis in rabbits is different from the one seen in rodents [75]. There- 386 fore, more studies are needed to elucidate the role of SR-BI in 387 regulating atherosclerosis. 388

Multiple factors regulate SR-BI expression (Fig. 3). Resveratrol 389 (Res), a bioactive molecule used in dietary supplements, and 390 13-hydroxy linoleic acid (LA), a natural PPAR agonist, induce SR-BI 391 expression in macrophages through PPAR^/LXRa pathway [76,77]. 392 Uto-Kondo et al. recently reported that coffee intake significantly 393


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx

394 increases SR-BI expression and HDL-mediated cholesterol efflux from

395 macrophages via its plasma phenolic acids [78]. Hydrogen administra-

396 tion also raises macrophage SR-BI levels in apoE-/- mice [79]. On the

397 other hand, pregnancy-associated plasma protein-A (PAPP-A), a

398 newly recognized metalloproteinase in the insulin-like growth factor

399 (IGF) system, significantly decreases SR-BI expression and promotes

400 the formation of macrophage foam cells via IGF-1/PI3K/Akt/LXRa

401 signaling pathway, indicating a novel mechanism for its proatherogenic

402 effect [80].

403 5. Conclusion and future directions

404 The balanced of cholesterol influx, esterification and release is nec-

405 essary to avoid lipid overload within macrophages, and ultimately,

406 atheroma development. Under atherogenic conditions, efflux of cho-

407 lesterol is decreased due to reduced expression of ABCA1, ABCG1

408 and SR-BI; however its uptake is increased due to enhanced expres-

409 sion of CD36 and SR-A as well as excess esterification of cholesterol oc-

410 curs because of higher ACAT1 level and lower nCEH level. This leads to

411 excessive CE accumulation as lipid droplets in macrophages, thereby

412 contributing to the formation of foam cells (Fig. 4). Therefore,

413 targeting these three pathways could be a viable approach to regulate

414 cholesterol metabolism in macrophages and treat atherosclerotic car-

415 diovascular diseases. K-604 and rimonabant, recently identified as po-

416 tent inhibitors of ACAT1, have been shown to inhibit macrophage

417 foam cell formation and retard atherosclerosis in apoE-/- mice Acknowledgment

418 [81,82]. A growing body of evidence indicates that food components

419 play an important role in prevention of foam cell formation by reduc-

420 ing cholesterol uptake and/or promoting its removal. For instance,

421 seven phenolic acids, the major bioactive compounds in blueberries,

have been recently reported to attenuate the formation of macro- 422

phage foam cells through downregulation of CD36 expression and 423

upregulation of ABCA1 expression [83]. Notably, despite strong 424

inverse association of plasma HDL levels with the risks of atheroscle- 425

rotic cardiovascular diseases, HDL-raising therapies are not always 426

effective. A randomized and placebo-controlled intervention trial has 427

demonstrated that niacin increases HDL-C but does not reduce cardio- 428

vascular events [84]. Moreover, a large human genetics study shows 429

that genetic variants that enhance HDL-C levels do not necessarily as- 430

sociate with myocardial infarction risk [85]. As a result, additional 431

studies are needed to evaluate the role of new compounds to raise 432

HDL-C levels or modify HDL composition and functionality. In addition 433

to these receptors, enzymes and transporters, we should pay attention 434

to the role of other molecules in cholesterol trafficking. In summary, 435

further work is required to elucidate the diverse processes that regu- 436

late the expression and activity of these proteins, and to determine 437

their contribution to disease protection in humans. These studies 438

will provide more insight into their physiological roles and will reveal 439

novel therapeutic strategies for treating atherosclerotic cardiovascular 440

disease. 441

Disclosure 443

The authors have declared no conflict of interest. 445

The authors gratefully acknowledge the financial support from 447 the National Natural Sciences Foundation of China (81070220 and 448 81170278), and Aid Program for Science and Technology Innovative 449


Fig. 4. Schematic representation of the mechanism involved in macrophage foam cell formation. Under atherogenic conditions, the increased uptake and esterification of cholesterol and/or reduced cholesterol efflux lead to excessive CE accumulation in the form of lipid droplets in the cytoplasm, thereby promoting the formation of macrophage foam cells. (+): activation, (-): inhibition.


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx

Research Team in Higher Educational Institutions of Human Province, China (2008-244).


Collot-Teixeira S, Martin J, McDermott-Roe C, Poston R, McGregor JL. CD36 and macrophages in atherosclerosis. Cardiovasc Res 2007;75:468-77. Ghosh S, Zhao B, Bie J, Song J. Macrophage cholesteryl ester mobilization and atherosclerosis. Vascul Pharmacol 2010;52:1-10.

Jessup W, Gelissen IC, Gaus K, Kritharides L. Roles of ATP binding cassette transporters A1 and G1, scavenger receptor BI and membrane lipid domains in cholesterol export from macrophages. Curr Opin Lipidol 2006;17:247-57. Kunjathoor VV, Febbraio M, Podrez EA, et al. Scavenger receptors class A-I/II and CD36 are the principal receptors responsible for the uptake of modified low density lipoprotein leading to lipid loading in macrophages. J Biol Chem 2002;277: 49982-8.

Handberg A, Hojlund K, Gastaldelli A, et al. Plasma sCD36 is associated with markers of atherosclerosis, insulin resistance and fatty liver in a nondiabetic healthy population. J Intern Med 2012;271:294-304.

Piechota M, Banaszewska A, Dudziak J, Slomczynski M, Plewa R Highly upregulated expression of CD36 and MSR1 in circulating monocytes of patients with acute coronary syndromes. Protein J 2012;31:511-8.

Geloen A, Helin L, Geeraert B, Malaud E, Holvoet P, Marguerie G. CD36 inhibitors reduce postprandial hypertriglyceridemia and protect against diabetic dyslipidemia and atherosclerosis. PLoS One 2012;7:e37633.

Rac ME, Safranow K, Rac M, et al. CD36 gene is associated with thickness of atheromatous plaque and ankle-brachial index in patients with early coronary artery disease. Kardiol Pol 2012;70:918-23.

Moore KJ, Kunjathoor VV, Koehn SL, et al. Loss of receptor-mediated lipid uptake via scavenger receptor A or CD36 pathways does not ameliorate atherosclerosis in hyperlipidemic mice. J Clin Invest 2005;115:2192-201.

Yuasa-Kawase M, Masuda D, Yamashita T, et al. Patients with CD36 deficiency are associated with enhanced atherosclerotic cardiovascular diseases. J Atheroscler Thromb 2012;19:263-75.

Inoue M, Tanabe H, Matsumoto A, et al. Astaxanthin functions differently as a selective peroxisome proliferator-activated receptor gamma modulator in adipocytes and macrophages. Biochem Pharmacol 2012;84:692-700. Mimche PN, Thompson E, Taramelli D, Vivas L. Curcumin enhances non-opsonic phagocytosis of Plasmodium falciparum through up-regulation of CD36 surface expression on monocytes/macrophages. J Antimicrob Chemother 2012;67:1895-904. Gao D, Pararasa C, Dunston CR, Bailey CJ, Griffiths HR Palmitate promotes monocyte atherogenicity via de novo ceramide synthesis. Free Radic Biol Med 2012;53: 796-806.

Goncalves JL, Roma EH, Gomes-Santos AC, et al. Pro-inflammatory effects of the mushroom Agaricus blazei and its consequences on atherosclerosis development. EurJNutr 2012;51:927-37.

Choi JS, Bae JY, Kim DS, et al. Dietary compound quercitrin dampens VEGF induction and PPARgamma activation in oxidized LDL-exposed murine macrophages: association with scavenger receptor CD36. J Agric Food Chem 2010;58:1333-41. Tang FT, Cao Y, Wang TQ, et al. Tanshinone IIA attenuates atherosclerosis in ApoE(-/-) mice through down-regulation of scavenger receptor expression. Eur J Pharmacol 2011;650:275-84.

Chiurchiu V, Izzi V, D'Aquilio F, et al. Endomorphin-1 prevents lipid accumulation via CD36 down-regulation and modulates cytokines release from human lipid-laden macrophages. Peptides 2011;32:80-5.

Granados-Principal S, Quiles JL, Ramirez-Tortosa CL, et al. Squalene ameliorates atherosclerotic lesions through the reduction of CD36 scavenger receptor expression in macrophages. Mol Nutr Food Res 2012;56:733-40. Li XY, Kong LX, Li J, He HX, Zhou YD. Kaempferol suppresses lipid accumulation in macrophages through the downregulation of cluster of differentiation 36 and the upregulation of scavenger receptor class B type I and ATP-binding cassette transporters A1 and G1. IntJ Mol Med 2013;31:331-8.

Nergiz-Unal R, Kuijpers MJ, de Witt SM, et al. Atheroprotective effect of dietary walnut intake in ApoE-deficient mice: involvement of lipids and coagulation factors. Thromb Res 2013;131:411-7.

Chu EM, Tai DC, Beer JL, Hill JS. Macrophage heterogeneity and cholesterol homeostasis: classically-activated macrophages are associated with reduced cholesterol accumulation following treatment with oxidized LDL. Biochim Biophys Acta 1831;2013:378-86.

Dai XY, Cai Y, Mao DD, et al. Increased stability of phosphatase and tensin homolog by intermedin leading to scavenger receptor A inhibition of macrophages reduces atherosclerosis in apolipoprotein E-deficient mice. J Mol Cell Cardiol 2012;53:509-20.

Makinen PI, Lappalainen JP, Heinonen SE, et al. Silencing of either SR-A or CD36 reduces atherosclerosis in hyperlipidaemic mice and reveals reciprocal upregulation of these receptors. Cardiovasc Res 2010;88:530-8.

Manning-Tobin JJ, Moore KJ, Seimon TA, et al. Loss of SR-A and CD36 activity reduces atherosclerotic lesion complexity without abrogating foam cell formation in hyperlipidemic mice. Arterioscler Thromb Vasc Biol 2009;29:19-26. Li K, Yao W, Zheng X, Liao K. Berberine promotes the development of atherosclerosis and foam cell formation by inducing scavenger receptor A expression in macrophage. Cell Res 2009;19:1006-17.

Hashizume M, Mihara M. Atherogenic effects of TNF-alpha and IL-6 via up-regulation of scavenger receptors. Cytokine 2012;58:424-30.

[28 [29

[32 [33

[35 [36

[40 [41

[46 [47

[50 [51

[53 [54 [55

Yang Y, Wang YF, Yang XF, et al. Specific Kv1.3 blockade modulates key cholesterol-metabolism-associated molecules in human macrophages exposed to ox-LDL. J Lipid Res 2013;54:34-43.

Zhao ZZ, Wang Z, Li GH, et al. Hydrogen sulfide inhibits macrophage-derived foam cell formation. Exp Biol Med (Maywood) 2011;236:169-76. Zhao JF, Ching LC, Huang YC, et al. Molecular mechanism of curcumin on the suppression of cholesterol accumulation in macrophage foam cells and atherosclerosis. Mol Nutr Food Res 2012;56:691-701.

Yang MY, Huang CN, Chan KC, Yang YS, Peng CH, Wang CJ. Mulberry leaf polyphenols possess antiatherogenesis effect via inhibiting LDL oxidation and foam cell formation. J Agric Food Chem 2011;59:1985-95.

Okazaki H, Igarashi M, Nishi M, et al. Identification of neutral cholesterol ester hydrolase, a key enzyme removing cholesterol from macrophages. J Biol Chem 2008;283:33357-64.

Dove DE, Su YR, Swift LL, Linton MF, Fazio S. ACAT1 deficiency increases cholesterol synthesis in mouse peritoneal macrophages. Atherosclerosis 2006;186:267-74. Yang L, Yang JB, Chen J, et al. Enhancement of human ACAT1 gene expression to promote the macrophage-derived foam cell formation by dexamethasone. Cell Res 2004;14:315-23.

Kusunoki J, Hansoty DK, Aragane K, Fallon JT, Badimon JJ, Fisher EA. Acyl-CoA:cho-lesterol acyltransferase inhibition reduces atherosclerosis in apolipoprotein E-deficient mice. Circulation 2001;103:2604-9.

Fazio S, Major AS, Swift LL, et al. Increased atherosclerosis in LDL receptor-null mice lacking ACAT1 in macrophages. J Clin Invest 2001;107:163-71. Su YR, Dove DE, Major AS, et al. Reduced ABCA1-mediated cholesterol efflux and accelerated atherosclerosis in apolipoprotein E-deficient mice lacking macrophage-derived ACAT1. Circulation 2005;111:2373-81.

Duewell P, Kono H, Rayner KJ, et al. NLRP3 inflammasomes are required for atherogenesis and activated by cholesterol crystals. Nature 2010;464:1357-61. Ge J, Zhai W, Cheng B, et al. Insulin induces human acyl-coenzyme A: cholesterol acyltransferase1 gene expression via MAP kinases and CCAAT/enhancer-binding protein alpha. J Cell Biochem 2013 [Epub ahead of print]. Liu W, He P, Cheng B, Mei CL, Wang YF, Wan JJ. Chlamydia pneumoniae disturbs cholesterol homeostasis in human THP-1 macrophages via JNK-PPARgamma dependent signal transduction pathways. Microbes Infect 2010;12:1226-35. Hongo S, Watanabe T, Arita S, et al. Leptin modulates ACAT1 expression and cholesterol efflux from human macrophages. Am J Physiol Endocrinol Metab 2009;297:E474-82. Hayashi K, Sasamura H, Azegami T, Itoh H. Regression of atherosclerosis in apoli-poprotein E-deficient mice is feasible using high-dose angiotensin receptor blocker, candesartan. J Atheroscler Thromb 2012;19:736-46. Nagashima M, Watanabe T, Terasaki M, et al. Native incretins prevent the development of atherosclerotic lesions in apolipoprotein E knockout mice. Diabetologia 2011;54:2649-59.

Cheng B, Wan J, Wang Y, et al. Ghrelin inhibits foam cell formation via simultaneously down-regulating the expression ofacyl-coenzyme A:cholesterol acyltransferase 1 and up-regulating adenosine triphosphate-binding cassette transporter A1. Cardiovasc Pathol 2010;19:e159-66.

Igarashi M, Osuga J, Isshiki M, et al. Targeting of neutral cholesterol ester hydro-lase to the endoplasmic reticulum via its N-terminal sequence. J Lipid Res 2010;51:274-85.

Igarashi M, Osuga J, Uozaki H, et al. The critical role of neutral cholesterol ester hydrolase 1 in cholesterol removal from human macrophages. Circ Res 2010;107: 1387-95.

Sekiya M, Osuga J, Nagashima S, et al. Ablation of neutral cholesterol ester hydro-lase 1 accelerates atherosclerosis. Cell Metab 2009;10:219-28. Zhao B, Song J, Chow WN, St Clair RW, Rudel LL, Ghosh S. Macrophage-specific transgenic expression of cholesteryl ester hydrolase significantly reduces atherosclerosis and lesion necrosis in Ldlr mice. J Clin Invest 2007;117:2983-92. Napolitano M, Avella M, Botham KM, Bravo E. Chylomicron remnant induction of lipid accumulation in J774 macrophages is associated with up-regulation of triacylglycerol synthesis which is not dependent on oxidation of the particles. Biochim Biophys Acta 2003;1631:255-64.

Yamashita M, Tamasawa N, Matsuki K, et al. Insulin suppresses HDL-mediated cholesterol efflux from macrophages through inhibition of neutral cholesteryl ester hydrolase and ATP-binding cassette transporter G1 expressions. J Atheroscler Thromb 2010;17:1183-9.

McLaren JE, Michael DR, Salter RC, et al. IL-33 reduces macrophage foam cell formation. J Immunol 2010;185:1222-9.

Miller AM, Liew FY. The IL-33/ST2 pathway — a new therapeutic target in cardiovascular disease. Pharmacol Ther 2011;131:179-86.

Bochem AE, van Wijk DF, Holleboom AG, et al. ABCA1 mutation carriers with low high-density lipoprotein cholesterol are characterized by a larger atherosclerotic burden. Eur Heart J 2013;34:286-91.

Zhao Y, Pennings M, Vrins CL, et al. Hypocholesterolemia, foam cell accumulation, but no atherosclerosis in mice lacking ABC-transporter A1 and scavenger receptor BI. Atherosclerosis 2011;218:314-22.

Joyce CW, Wagner EM, Basso F, et al. ABCA1 overexpression in the liver of LDLr-KO mice leads to accumulation of pro-atherogenic lipoproteins and enhanced atherosclerosis. J Biol Chem 2006;281:33053-65. Lee SM, Moon J, Cho Y, Chung JH, Shin MJ. Quercetin up-regulates expressions of peroxisome proliferator-activated receptor gamma, liver X receptor alpha, and ATP binding cassette transporter A1 genes and increases cholesterol efflux in human macrophage cell line. Nutr Res 2013;33:136-43.

Liu XY, Lu Q, Ouyang XP, et al. Apelin-13 increases expression of ATP-binding cassette transporter A1 via activating protein kinase C alpha signaling in THP-1 macrophage-derived foam cells. Atherosclerosis 2013;226:398-407.


X. Yu et al. / Clinica Chimica Acta xxx (2013) xxx-xxx

[59 [60

[64 [65 [66 [67 [68

[69 [70

Park DW, Lee HK, Lyu JH, et al. TLR2 stimulates ABCA1 expression via PKC-eta and [71 PLD2 pathway. Biochem Biophys Res Commun 2013;430:933-7. Malekpour-Dehkordi Z, Javadi E, Doosti M, et al. S-allylcysteine, a garlic compound, increases ABCA1 expression in human THP-1 macrophages. Phytother [72 Res 2013;27:357-61.

Ku CS, Park Y, Coleman SL, Lee J. Unsaturated fatty acids repress expression of ATP [73 binding cassette transporter A1 and G1 in RAW 264.7 macrophages. J Nutr Biochem 2012;23:1271-6.

Yu XH, Jiang HL, Chen WJ, et al. Interleukin-18 and interleukin-12 together down- [74 regulate ATP-binding cassette transporter A1 expression through the interleukin-18R/nuclear factor-kappaB signaling pathway in THP-1 macrophage-derived foam cells. CircJ 2012;76:1780-91. [75

Sun D, Zhang J, Xie J, Wei W, Chen M, Zhao X. MiR-26 controls LXR-dependent cholesterol efflux by targeting ABCA1 and ARL7. FEBS Lett 2012;586:1472-9. Schou J, Frikke-Schmidt R, Kardassis D, et al. Genetic variation in ABCG1 and risk [76 of myocardial infarction and ischemic heart disease. Arterioscler Thromb Vasc Biol 2012;32:506-15.

Out R, Hoekstra M, Hildebrand RB, et al. Macrophage ABCG1 deletion disrupts [77 lipid homeostasis in alveolar macrophages and moderately influences atherosclerotic lesion development in LDL receptor-deficient mice. Arterioscler Thromb Vasc Biol 2006;26:2295-300.

Ranalletta M, Wang N, Han S, Yvan-Charvet L, Welch C, Tall AR. Decreased athero- [78 sclerosis in low-density lipoprotein receptor knockout mice transplanted with Abcg1-/- bone marrow. Arterioscler Thromb Vasc Biol 2006;26:2308-15. [79

Baldan A, Pei L, Lee R, et al. Impaired development of atherosclerosis in hyperlip-idemic Ldlr-/- and ApoE-/- mice transplanted with Abcg1-/- bone marrow. Arterioscler Thromb Vasc Biol 2006;26:2301-7. [80

Meurs I, Lammers B, Zhao Y, et al. The effect of ABCG1 deficiency on atherosclerotic lesion development in LDL receptor knockout mice depends on the stage of athero-genesis. Atherosclerosis 2012;221:41-7. [81

Jun HJ, Hoang MH, Yeo SK, Jia Y, Lee SJ. Induction of ABCA1 and ABCG1 expression by the liver X receptor modulator cineole in macrophages. Bioorg Med Chem Lett 2013;23:579-83. [82

Hoang MH, Jia Y, Jun HJ, Lee JH, Lee BY, Lee SJ. Fucosterol is a selective liver X receptor modulator that regulates the expression of key genes in cholesterol [83 homeostasis in macrophages, hepatocytes, and intestinal cells. J Agric Food Chem 2012;60:11567-75.

Helal O, Berrougui H, Loued S, Khalil A. Extra-virgin olive oil consumption [84 improves the capacity of HDL to mediate cholesterol efflux and increases ABCA1 and ABCG1 expression in human macrophages. Br J Nutr 2012:1-12. [85

Wang D, Xia M, Yan X, et al. Gut microbiota metabolism of anthocyanin promotes reverse cholesterol transport in mice via repressing miRNA-10b. Circ Res 2012;111: 967-81.

Maitra U, Li L. Molecular mechanisms responsible for the reduced expression of 661

cholesterol transporters from macrophages by low-dose endotoxin. Arterioscler 662

Thromb Vasc Biol 2013;33:24-33. 663

Vergeer M, Korporaal SJ, Franssen R, et al. Genetic variant of the scavenger recep- 664

tor BI in humans. N Engl J Med 2011;364:136-45. 665

Zhang W, Yancey PG, Su YR, et al. Inactivation of macrophage scavenger receptor 666

class B type I promotes atherosclerotic lesion development in apolipoprotein 667

E-deficient mice. Circulation 2003;108:2258-63. 668

Van Eck M, Bos IS, Hildebrand RB, Van Rij BT, Van Berkel TJ. Dual role for scavenger 669

receptor class B, type I on bone marrow-derived cells in atherosclerotic lesion devel- 670

opment Am J Pathol 2004;165:785-94. 671

Demetz E, Tancevski I, Duwensee K, et al. Inhibition of hepatic scavenger 672

receptor-class B type I by RNA interference decreases atherosclerosis in rabbits. 673

Atherosclerosis 2012;222:360-6. 674

Voloshyna I, Hai O, Littlefield MJ, Carsons S, Reiss AB. Resveratrol mediates 675

anti-atherogenic effects on cholesterol flux in human macrophages and endothe- 676

lium via PPARgamma and adenosine. Eur J Pharmacol 2013;698:299-309. 677

Kammerer I, Ringseis R, Biemann R, Wen G, Eder K. 13-hydroxy linoleic acid in- 678

creases expression of the cholesterol transporters ABCA1, ABCG1 and SR-BI and 679

stimulates apoA-I-dependent cholesterol efflux in RAW264.7 macrophages. Lipids 680

Health Dis 2011;10:222-9. 681

Uto-Kondo H, Ayaori M, Ogura M, et al. Coffee consumption enhances high-density 682

lipoprotein-mediated cholesterol efflux in macrophages. Circ Res 2010;106:779-87. 683

Song G, Tian H, Qin S, et al. Hydrogen decreases athero-susceptibility in apolipo- 684

protein B-containing lipoproteins and aorta of apolipoprotein E knockout mice. 685

Atherosclerosis 2012;221:55-65. 686

Tang SL, Chen WJ, Yin K, et al. PAPP-A negatively regulates ABCA1, ABCG1 and 687

SR-B1 expression by inhibiting LXRalpha through the IGF-I-mediated signaling 688

pathway. Atherosclerosis 2012;222:344-54. 689

Yoshinaka Y, Shibata H, Kobayashi H, et al. A selective ACAT-1 inhibitor, K-604, 690

stimulates collagen production in cultured smooth muscle cells and alters plaque 691

phenotype in apolipoprotein E-knockout mice. Atherosclerosis 2010;213:85-91. 692

Netherland C, Thewke DP. Rimonabant is a dual inhibitor of acyl CoA:cholesterol 693

acyltransferases 1 and 2. Biochem Biophys Res Commun 2010;398:671 -6. 694

Xie C, Kang J, Chen JR, Nagarajan S, Badger TM, Wu X. Phenolic acids are in vivo 695

atheroprotective compounds appearing in the serum of rats after blueberry con- 696

sumption. J Agric Food Chem 2011;59:10381-7. 697

Boden WE, Probstfield JL, Anderson T, et al. Niacin in patients with low HDL cho- 698

lesterol levels receiving intensive statin therapy. N Engl J Med 2011;365:2255-67. 699

Voight BF, Peloso GM, Orho-Melander M, et al. Plasma HDL cholesterol and risk of 700

myocardial infarction: a mendelian randomisation study. Lancet 2012;380:572-80. 701