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Background and Aims: Scavenger receptor class B1 (SCARB1) - also known as the high-density lipoprotein (HDL) receptor - is a multi-ligand scavenger receptor that is primarily expressed in liver and steroidogenic organs. This receptor is known for its function in reverse cholesterol transport (RCT) in mammals and hence disruption leads to a massive increase in HDL cholesterol in these species. The extracellular domain of SCARB1 - which is important for cholesterol handling - is highly conserved across multiple vertebrates, except in zebrafish., Methods: To examine the functional conservation of SCARB1 among vertebrates, two stable scarb1 knockout zebrafish lines, scarb1 715delA (scarb1 -1 nt) and scarb1 715&#95;716insGG (scarb1 +2 nt), were created using CRISPR-Cas9 technology., Results: We demonstrate that, in zebrafish, SCARB1 deficiency leads to disruption of carotenoid-based pigmentation, reduced fertility, and a decreased larvae survival rate, whereas steroidogenesis was unaltered. The observed reduced fertility is driven by defects in female fertility (-50 %, p < 0.001). Importantly, these alterations were independent of changes in free (wild-type 2.4 ± 0.2 μg/μl versus scarb1 -/- 2.0 ± 0.1 μg/μl) as well as total (wild-type 4.2 ± 0.4 μg/μl versus scarb1 -/- 4.0 ± 0.3 μg/μl) plasma cholesterol levels. Uptake of HDL in the liver of scarb1 -/- zebrafish larvae was reduced (-86.7 %, p < 0.001), but this coincided with reduced perfusion of the liver. No effect was observed on lipoprotein uptake in the caudal vein. SCARB1 deficient canaries, which also lack carotenoids in their plumage, similarly as scarb1 -/- zebrafish, failed to show an increase in plasma free- and total cholesterol levels., Conclusion: Our findings suggest that the specific function of SCARB1 in maintaining plasma cholesterol could be an evolutionary novelty that became prominent in mammals, while other known functions were already present earlier during vertebrate evolution., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Apolipoprotein M (ApoM) exhibits various anti-atherosclerotic functions as a component of high-density lipoprotein (HDL) particles. Scavenger receptor class B type I (SR-BI) is a classic HDL receptor that mediates selective cholesterol uptake and enhances the efflux of cellular cholesterol to HDL. However, the effect of ApoM on cholesterol transport in macrophages remains unclear. In this study, we identified for the first time that ApoM is expressed in mouse macrophages and is involved in cholesterol uptake, similar to SR-BI. NBD-cholesterol uptake and efflux in cells were characterized using fluorescence spectrophotometry. The uptake ratios of cholesterol by macrophages from ApoM -/- SR-BI -/- mice were significantly lower than those from ApoM +/+ SR-BI -/- and ApoM -/- SR-BI +/+ mice. Real-time fluorescence quantitative PCR was used to analyze the expression of cholesterol transport-related genes involved in cholesterol uptake. ApoM-enriched HDL (ApoM + HDL) facilitated more cholesterol efflux from murine macrophage Ana-1 cells than ApoM-free HDL (ApoM - HDL). However, recombinant human ApoM protein inhibited the ability of ApoM - HDL to induce cholesterol efflux. In conclusion, ApoM promotes cholesterol uptake and efflux in mouse macrophages. A better understanding of ApoM function may lead to the development of novel therapeutic strategies for treating atherosclerotic diseases., (© 2021 The Authors. FEBS Open Bio published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

During pregnancy, extravillous trophoblasts (EVTs) invade the maternal decidua and remodel the local vasculature to establish blood supply for the growing fetus. Compromised EVT function has been linked to aberrant pregnancy associated with maternal and fetal morbidity and mortality. However, metabolic features of this invasive trophoblast subtype are largely unknown. Using primary human trophoblasts isolated from first trimester placental tissues, we show that cellular cholesterol homeostasis is differentially regulated in EVTs compared with villous cytotrophoblasts. Utilizing RNA-sequencing, gene set-enrichment analysis, and functional validation, we provide evidence that EVTs display increased levels of free and esterified cholesterol. Accordingly, EVTs are characterized by increased expression of the HDL-receptor, scavenger receptor class B type I, and reduced expression of the LXR and its target genes. We further reveal that EVTs express elevated levels of hydroxy-delta-5-steroid dehydrogenase 3 beta- and steroid delta-isomerase 1 (HSD3B1) (a rate-limiting enzyme in progesterone synthesis) and are capable of secreting progesterone. Increasing cholesterol export by LXR activation reduced progesterone secretion in an ABCA1-dependent manner. Importantly, HSD3B1 expression was decreased in EVTs of idiopathic recurrent spontaneous abortions, pointing toward compromised progesterone metabolism in EVTs of early miscarriages. Here, we provide insights into the regulation of cholesterol and progesterone metabolism in trophoblastic subtypes and its putative relevance in human miscarriage., (Copyright © 2019 Vondra et al.)

Curcumin, which is an extract from a traditional Chinese medicine, has previously been demonstrated to exhibit an anti‑atherosclerotic effect, which is closely associated with an increase in cholesterol efflux. However, it is unclear as to whether the increased effect is mediated by heme oxygenase (HO)‑1. Macrophages were treated with different concentrations of curcumin, HO‑1 inhibitor and small interfering (si)RNA in different experiments. Analysis of protein expression was conducted via western blotting. mRNA expression levels were measured using reverse transcription‑polymerase chain reaction. Antioxidant response element (ARE)‑driven promoter activity was measured by a dual‑luciferase reporter assay. The cholesterol efflux analysis was performed by fluorescence‑labelled cholesterol (NBD) using a multi‑label counter. In the present study, the results indicated that curcumin increased the cholesterol efflux from macrophages. Additionally, curcumin significantly upregulated HO‑1 expression. The HO‑1 inhibitor (zinc protoporphyrin) partly blocked this effect. Curcumin also promoted scavenger receptor class B type I (SR‑BI) and ATP‑binding cassette transporter A1 (ABCA1) expression. HO‑1 small interfering (si)RNA partly abolished the increased SR‑BI and ABCA1 expression induced by curcumin. Furthermore, the nuclear factor, erythroid 2 like 2 (Nrf2) expression in the nucleus was dose‑dependently increased by curcumin. Nrf2 siRNA successfully inhibited the curcumin‑induced HO‑1 expression. Curcumin significantly increased Nrf2‑driven luciferase activity. Overall, these data indicated that curcumin activates the Nrf2‑ARE signaling pathway and upregulates HO‑1 expression, which mediates SR‑BI and ABCA1 expression and thereby increases cholesterol efflux.

Scavenger receptors (SRs) like cluster determinant 36 (CD36) and SR class B type I (SR-BI) play a debated role in lipid transport across the intestinal brush border membrane. We used surface plasmon resonance to analyze real-time interactions between the extracellular protein loops and various ligands ranging from single lipid molecules to mixed micelles. Micelles mimicking physiological structures were necessary for optimal binding to both the extracellular loop of CD36 (lCD36) and the extracellular loop of SR-BI (lSR-BI). Cholesterol, phospholipid, and fatty acid micellar content significantly modulated micelle binding to and dissociation from the transporters. In particular, high phospholipid micellar concentrations inhibited micelle binding to both receptors (-53.8 and -74.4% binding at 0.32 mM compared with 0.04 mM for lCD36 and lSR-BI, respectively, P < 0.05). The presence of fatty acids was crucial for micelle interactions with both proteins (94.4 and 81.3% binding with oleic acid for lCD36 and lSR-BI, respectively, P < 0.05) and fatty acid type substitution within the micelles was the component that most impacted micelle binding to the transporters. These effects were partly due to subsequent modifications in micellar size and surface electric charge, and could be correlated to micellar vitamin D uptake by Caco-2 cells. Our findings show for the first time that micellar lipid composition and micellar properties are key factors governing micelle interactions with SRs., (Copyright © 2015 by the American Society for Biochemistry and Molecular Biology, Inc.)

The ability of HDL to support macrophage cholesterol efflux is an integral part of its atheroprotective action. Augmenting this ability, especially when HDL cholesterol efflux capacity from macrophages is poor, represents a promising therapeutic strategy. One approach to enhancing macrophage cholesterol efflux is infusing blood with HDL mimics. Previously, we reported the synthesis of a functional mimic of HDL (fmHDL) that consists of a gold nanoparticle template, a phospholipid bilayer, and apo A-I. In this work, we characterize the ability of fmHDL to support the well-established pathways of cellular cholesterol efflux from model cell lines and primary macrophages. fmHDL received cell cholesterol by unmediated (aqueous) and ABCG1- and scavenger receptor class B type I (SR-BI)-mediated diffusion. Furthermore, the fmHDL holoparticle accepted cholesterol and phospholipid by the ABCA1 pathway. These results demonstrate that fmHDL supports all the cholesterol efflux pathways available to native HDL and thus, represents a promising infusible therapeutic for enhancing macrophage cholesterol efflux. fmHDL accepts cholesterol from cells by all known pathways of cholesterol efflux: unmediated, ABCG1- and SR-BI-mediated diffusion, and through ABCA1., (Copyright © 2015 by the American Society for Biochemistry and Molecular Biology, Inc.)

Aim: To characterize cholesterol regulation in the liver of patients with Alagille syndrome (AGS)., Methods: Serum total cholesterol (TC) and total bile acid (TBA) levels were measured in 23 AGS patients. The expressions of genes involved in cholesterol regulation, including low-density lipoprotein receptor (LDLR), scavenger receptor class B type I (SR-BI), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), cholesterol 7α-hydroxylase (CYP7A1), ATP-binding cassette transporter (ABC) A1, and ABCG1/5/8, were measured in liver tissues from five of these patients. Expression of regulators for these genes, including farnesoid X receptor/small heterodimer partner (SHP), liver X receptor α (LXRα) and mature Sterol regulatory element-binding protein 2 (SREBP2) was measured. The expression of mature SREBP2 protein was also examined., Results: Serum TC and TBA levels were correlated in the AGS patients. Liver cholesterol was also increased compared with controls, and correlated with bile acid contents. LDLR, SR-BI, HMGCR, and ABCGs mRNA expression were upregulated, while CYP7A1 mRNA expression was downregulated in AGS livers. SHP and LXRα mRNA expression was also increased, but maturation of SREBP2 was not suppressed in the patients., Conclusions: The major upregulators of liver cholesterol might be increased in AGS patients, indicating an impaired negative feedback mechanism and accelerated liver cholesterol accumulation., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Objective: Serum amyloid A (SAA) is an acute phase response protein and has apolipoprotein properties. Since type 2 diabetes is associated with chronic subclinical inflammation, the objective of this study is to investigate the changes in SAA level in type 2 diabetic patients and to evaluate the relationship between SAA and the capacity of serum to induce cellular cholesterol efflux via the two known cholesterol transporters, scavenger receptor class B type I (SR-BI) and ATP-binding cassette transporter G1 (ABCG1)., Methods: 264 patients with type 2 diabetes mellitus (42% with normoalbuminuria, 30% microalbuminuria, and 28% proteinuria) and 275 non-diabetic controls were recruited. SAA was measured by ELISA. SR-BI and ABCG1-mediated cholesterol efflux to serum were determined by measuring the transfer of [(3)H]cholesterol from Fu5AH rat hepatoma cells expressing SR-BI and from human ABCG1-transfected CHO-K1 cells to the medium containing the tested serum respectively., Results: SAA was significantly increased in diabetic patients with incipient or overt nephropathy. Both SR-BI and ABCG1-mediated cholesterol efflux to serum were significantly impaired in all three groups of diabetic patients (p < 0.01). SAA inversely correlated with SR-BI-mediated cholesterol efflux (r = -0.36, p < 0.01) but did not correlate with ABCG1-mediated cholesterol efflux. Stepwise linear regression analysis showed that HDL, the presence or absence of diabetes, and log(SAA) were significant independent determinants of SR-BI-mediated cholesterol efflux to serum., Conclusion: SAA was increased in type 2 diabetic patients with incipient or overt nephropathy, and SAA was associated with impairment of SR-BI-mediated cholesterol efflux to serum., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Reverse cholesterol transport (RCT) can proceed through the classic hepatobiliary route or through the nonbiliary transintestinal cholesterol efflux (TICE) pathway. Scavenger receptor class B type I (SR-BI) plays a critical role in the classic hepatobiliary route of RCT. However, the role of SR-BI in TICE has not been studied. To examine the role of intestinal SR-BI in TICE, sterol balance was measured in control mice and mice transgenically overexpressing SR-BI in the proximal small intestine (SR-BI(hApoCIII-ApoAIV-Tg)). SR-BI(hApoCIII-ApoAIV-Tg) mice had significantly lower plasma cholesterol levels compared with wild-type controls, yet SR-BI(hApoCIII-ApoAIV-Tg) mice had normal fractional cholesterol absorption and fecal neutral sterol excretion. Both in the absence or presence of ezetimibe, intestinal SR-BI overexpression had no impact on the amount of cholesterol excreted in the feces. To specifically study effects of intestinal SR-BI on TICE we crossed SR-BI(hApoCIII-ApoAIV-Tg) mice into a mouse model that preferentially utilized the TICE pathway for RCT (Niemann-Pick C1-like 1 liver transgenic), and likewise found no alterations in cholesterol absorption or fecal sterol excretion. Finally, mice lacking SR-BI in all tissues also exhibited normal cholesterol absorption and fecal cholesterol disposal. Collectively, these results suggest that SR-BI is not rate limiting for intestinal cholesterol absorption or for fecal neutral sterol loss through the TICE pathway.

Apolipoprotein M (ApoM) exhibits various anti‐atherosclerotic functions as a component of high‐density lipoprotein (HDL) particles. Scavenger receptor class B type I (SR‐BI) is a classic HDL receptor that mediates selective cholesterol uptake and enhances the efflux of cellular cholesterol to HDL. However, the effect of ApoM on cholesterol transport in macrophages remains unclear. In this study, we identified for the first time that ApoM is expressed in mouse macrophages and is involved in cholesterol uptake, similar to SR‐BI. NBD‐cholesterol uptake and efflux in cells were characterized using fluorescence spectrophotometry. The uptake ratios of cholesterol by macrophages from ApoM−/−SR‐BI−/− mice were significantly lower than those from ApoM+/+SR‐BI−/− and ApoM−/−SR‐BI+/+ mice. Real‐time fluorescence quantitative PCR was used to analyze the expression of cholesterol transport‐related genes involved in cholesterol uptake. ApoM‐enriched HDL (ApoM+HDL) facilitated more cholesterol efflux from murine macrophage Ana‐1 cells than ApoM‐free HDL (ApoM−HDL). However, recombinant human ApoM protein inhibited the ability of ApoM−HDL to induce cholesterol efflux. In conclusion, ApoM promotes cholesterol uptake and efflux in mouse macrophages. A better understanding of ApoM function may lead to the development of novel therapeutic strategies for treating atherosclerotic diseases.

Scavenger receptors (SRs) like cluster determinant 36 (CD36) and SR class B type I (SR-BI) play a debated role in lipid transport across the intestinal brush border membrane. We used surface plasmon resonance to analyze real-time interactions between the extracellular protein loops and various ligands ranging from single lipid molecules to mixed micelles. Micelles mimicking physiological structures were necessary for optimal binding to both the extracellular loop of CD36 (lCD36) and the extracellular loop of SR-BI (lSR-BI). Cholesterol, phospholipid, and fatty acid micellar content significantly modulated micelle binding to and dissociation from the transporters. In particular, high phospholipid micellar concentrations inhibited micelle binding to both receptors (−53.8 and −74.4% binding at 0.32 mM compared with 0.04 mM for lCD36 and lSR-BI, respectively, P < 0.05). The presence of fatty acids was crucial for micelle interactions with both proteins (94.4 and 81.3% binding with oleic acid for lCD36 and lSR-BI, respectively, P < 0.05) and fatty acid type substitution within the micelles was the component that most impacted micelle binding to the transporters. These effects were partly due to subsequent modifications in micellar size and surface electric charge, and could be correlated to micellar vitamin D uptake by Caco-2 cells. Our findings show for the first time that micellar lipid composition and micellar properties are key factors governing micelle interactions with SRs.

Intake of a high dosage of baicalin has previously been shown to attenuate hyperlipidemia induced by a high-fat diet. Baicalin functions as an activator of peroxisome proliferator-activated receptor-γ (PPAR-γ), which is the key regulator of reverse cholesterol transport (RCT). The present study aimed to test the hypothesis that baicalin could promote cholesterol efflux in macrophages through activating PPAR-γ. Phorbol 12-myristate 13-acetate-stimulated THP-1 cells were treated with oxidized low-density lipoprotein and (3H)-cholesterol for 24 h, and the effects of baicalin on cholesterol efflux were evaluated in the presence of apolipoprotein A-1 (ApoA-1), or high-density lipoprotein subfraction 2 (HDL2) or subfraction 3 (HDL3). The expression levels of scavenger receptor class B type I (SR-BI), PPAR-γ and liver X receptor-α (LXRα) were detected and specific inhibitors or activators of SR-BI, PPAR-γ and LXRα were applied to investigate the mechanism. Treatment of THP-1 macrophages with baicalin significantly accelerated HDL-mediated, but not ApoA-1-mediated cholesterol efflux. However, baicalin treatment increased the expression of SR-BI at the mRNA and protein levels in a dose- and time-dependent manner, and pre-treatment with the SR-BI inhibitor BLT-1 and SR-BI small interfering RNA significantly inhibited baicalin-induced cholesterol efflux. Furthermore, baicalin increased the expression of PPAR-γ and LXRα, and the application of specific agonists and inhibitors of PPAR-γ and LXRα changed the expression of SR-BI, as well as cholesterol efflux. It may be concluded that baicalin induced cholesterol efflux from THP-1 macrophages via the PPAR-γ/LXRα/SR-BI pathway. [ABSTRACT FROM AUTHOR]

Reduction of plasma LCAT activity has been observed in several conditions in which the size of HDL particles is increased; however, the mechanism of this reduction remains elusive. We investigated the plasma activity, mass, and in vivo catabolism of LCAT and its association with HDL particles in human apolipoprotein A-I transgenic, scavenger receptor class B type I knockout (hA-I Tg SR-BI−/−) mice. Compared with hA-I Tg mice, hA-I Tg SR-BI−/− mice had a 4-fold higher total plasma cholesterol concentration, which occurred predominantly in 13–18 nm diameter HDL particles, a significant reduction in plasma esterified cholesterol-total cholesterol (EC/TC) ratio, and significantly lower plasma LCAT activity, suggesting a decrease in LCAT protein. However, LCAT protein in plasma, hepatic mRNA for LCAT, and in vivo turnover of 35S-radiolabeled LCAT were similar in both genotypes of mice. HDL from hA-I Tg SR-BI−/− mice was enriched in sphingomyelin (SM), relative to phosphatidylcholine, and had less associated [35S]LCAT radiolabel and endogenous LCAT activity compared with HDL from hA-I Tg mice. We conclude that the decreased EC/TC ratio in the plasma of hA-I Tg SR-BI−/− mice is attributed to a reduction in LCAT reactivity with SM-enriched HDL particles.

Abstract: In order to investigate the effect and mechanism of action of rosuvastatin on atherosclerotic lesion in a Wistar rat model, 16 Wistar rats were fed a cholesterol-rich, vitamin D3 overload diet and underwent balloon injury of the aorta. One day prior to injury, half of the rats began rosuvastatin treatment (5mg/kg/d) via oral gavage. Eight control rats received a basal diet and sham operation. After 14 weeks of treatment, the animals were sacrificed. Blood was collected to measure lipid and angiotensin II (Ang II) levels and morphologic analysis was performed on the aorta. Scavenger receptor-class B type I (SR-BI), Ang II type-1 (AT1) receptor and phosphorylated extracellular signal regulated kinase 1/2 (p-ERK1/2) protein and mRNA levels were measured via Western blot and real time reverse transcriptase polymerase chain reaction, respectively. Spearman's rank correlation was utilized to examine the relationships between SR-BI and Ang II or AT1 receptor expression. The atherosclerosis model group demonstrated an increase in plasma lipid levels and aortic plaque formation. After 14 weeks of treatment with rosuvastatin, there was a significant decrease in plasma lipid and Ang II levels accompanied by an improvement in aortic lesions. Rosuvastatin increased the expression of SR-BI but significantly inhibited the expression of AT1 receptor and p-ERK1/2. SR-BI protein expression was inversely correlated with both the level of Ang II and expression of the AT1 receptor. In conclusion, rosuvastatin attenuates atherosclerosis in the Wistar rat model, and its anti-atherosclerotic activity may be through upregulation of SR-BI expression and inhibition of p-ERK1/2 levels and AT1 receptor expression. [Copyright &y& Elsevier]

The article discusses a study regarding the detection of the scavenger receptor class B type I gene exon 1 G4A gene polymorphism in patients with atherosclerotic cerebral infarction and hemorrhage using the polymerase chain reaction-restriction fragment length polymorphism method. Topics include the high serum level of high-density lipoprotein cholesterol in patients, atherosclerosis as a risk factor for stroke, and the prevalence of hypertension and diabetes mellitus in patients.

Biliary cholesterol secretion is a process important for 2 major disease complexes, atherosclerotic cardiovascular disease and cholesterol gallstone disease. With respect to cardiovascular disease, biliary cholesterol secretion is regarded as the final step for the elimination of cholesterol originating from cholesterol-laden macrophage foam cells in the vessel wall in a pathway named reverse cholesterol transport. On the other hand, cholesterol hypersecretion into the bile is considered the main pathophysiological determinant of cholesterol gallstone formation. This review summarizes current knowledge on the origins of cholesterol secreted into the bile as well as the relevant processes and transporters involved. Next to the established ATP-binding cassette (ABC) transporters mediating the biliary secretion of bile acids (ABCB11), phospholipids (ABCB4) and cholesterol (ABCG5/G8), special attention is given to emerging proteins that modulate or mediate biliary cholesterol secretion. In this regard, the potential impact of the phosphatidylserine flippase ATPase class I type 8B member 1, the Niemann Pick C1-like protein 1 that mediates cholesterol absorption and the high density lipoprotein cholesterol uptake receptor, scavenger receptor class B type I, is discussed. [ABSTRACT FROM AUTHOR]

Scavenger receptor class B type I (SR-BI) is an important member of the scavenger receptor family of integral membrane glycoproteins. This review highlights studies in SR-BI knockout mice, which concern the role of SR-BI in cholesterol and steroid metabolism. SR-BI in hepatocytes is the sole molecule involved in selective uptake of cholesteryl esters from high-density lipoprotein (HDL). SR-BI plays a physiological role in binding and uptake of native apolipoprotein B (apoB)-containing lipoproteins by hepatocytes, which identifies SR-BI as a multipurpose player in lipid uptake from the blood circulation into hepatocytes in mice. In adrenocortical cells, SR-BI mediates the selective uptake of HDL-cholesteryl esters, which is efficiently coupled to the synthesis of glucocorticoids (i.e. corticosterone). SR-BI knockout mice suffer from adrenal glucocorticoid insufficiency, which suggests that functional SR-BI protein is necessary for optimal adrenal steroidogenesis in mice. SR-BI in macrophages plays a dual role in cholesterol metabolism as it is able to take up cholesterol associated with HDL and apoBcontaining lipoproteins and can possibly facilitate cholesterol efflux to HDL. Absence of SR-BI is associated with thrombocytopenia and altered thrombosis susceptibility, which suggests a novel role for SR-BI in regulating platelet number and function in mice. Transgenic expression of cholesteryl ester transfer protein in humanized SR-BI knockout mice normalizes hepatic delivery of HDL-cholesteryl esters. However, other pathologies associated with SR-BI deficiency, i.e. increased atherosclerosis susceptibility, adrenal glucocorticoid insufficiency, and impaired platelet function are not normalized, which suggests an important role for SR-BI in cholesterol and steroid metabolism in man. In conclusion, generation of SR-BI knockout mice has significantly contributed to our knowledge of the physiological role of SR-BI. Studies using these mice have identified SR-BI as a multi-purpose player in cholesterol and steroid metabolism because it has distinct roles in reverse cholesterol transport, adrenal steroidogenesis, and platelet function. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To identify the genetic variant in the CETP gene of the proband with high HDL-C and low CETP activity and to investigate whether HDL from the CETP-deficient subject was dysfunctional in the reverse cholesterol transport (RCT) pathway. Methods: We sequenced the CETP gene and assessed its promoter activity. Cholesterol efflux and hepatic cholesteryl ester delivery studies were also performed using the proband''s HDL. Results: A proband was a compound heterozygote for a known D459G variant and a novel 18-bp deletion mutation in the CETP promoter. This promoter mutation markedly reduced the transcriptional activity in HepG2 cells. HDL2 from this subject increased SR-BI-mediated cholesterol efflux, whereas cholesteryl ester delivery into hepatocytes was maintained. Conclusion: A novel deletion mutation in the CETP promoter is associated with high HDL-C and decreased promoter activity. HDL from this CETP-deficient subject was not dysfunctional in mediating two main steps of RCT assessed in vitro. [Copyright &y& Elsevier]

dvanced prostate cancer (CaP) is often treated with androgen deprivation therapy (ADT). Despite high initial success rates of this therapy, recurrence of the cancer in a castration-resistant (CRPC) form is inevitable. It has been demonstrated that, despite the low levels of circulating androgens resulting from ADT, intratumoral androgen levels remain high and androgen receptor activation persists. Recently, it was discovered that de novo androgen synthesis is occurring within the tumor cells themselves, thus providing a potential mechanism for the high endogenous concentrations. A common upstream precursor in this steroidogenic pathway is cholesterol. For many decades, the breakdown of cholesterol homeostasis in cancer has been the focus of research, but this was largely to elucidate its involvement in maintaining membrane integrity and cell signaling. De novo steroidogenesis has provided a new avenue for cholesterol research and reinforces the importance of understanding the mechanisms that lead to the alterations in cholesterol regulation in the progression to CRPC. The findings to date suggest that cholesterol homeostasis is altered to support de novo androgen synthesis and appear to facilitate disease progression. We further propose that a better understanding of the link between cholesterol and de novo androgen synthesis in CaP progression may provide opportunities for novel therapeutic intervention, namely via eliminating sources of the precursor cholesterol. This review summarizes the implications of cholesterol dysregulation in CaP and particularly in the post-ADT castration-resistant state, as well as the potential implementation of novel therapies targeting these cholesterol sources. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The uptake of oxidized LDL (oxLDL) by macrophages is a key initial event in atherogenesis, and the removal of oxidized lipids from artery wall via reverse cholesterol transport is considered antiatherogenic. The aims of this study were to investigate the pathways mediating the removal of oxysterols from oxLDL-loaded macrophages, and the subsequent uptake of the oxysterols by hepatocytes. Methods: LDL was labeled with [3H]cholesterol, and LDL-[3H]cholesterol was oxidized by copper using a standard method. [3H]oxysterol formation in oxLDL was analyzed by thin layer chromatography. oxLDL-[3H]sterol was incubated with macrophages, allowing the uptake of [3H]sterol by macrophages. [3H]sterol efflux from macrophages mediated by ATP binding cassette transporters (ABCA1, ABCG1), or scavenger receptor class B type I (SR-BI) was measured. The subsequent uptake of the [3H]sterol by hepatocytes was also determined. Results: 7-Ketocholesterol was the major oxysterol formed in oxLDL, and it was significantly higher in oxLDL compared with that in native LDL (naLDL). oxLDL-derived sterol efflux to HDL from macrophages was significantly increased compared with naLDL-derived sterol, and it was mainly mediated by ABCG1, but not by ABCA1 or SR-BI. Moreover, although HDL dose-dependently induced sterol efflux from macrophages, only the exported sterol by ABCG1 pathway was efficiently taken up by hepatocytes. Conclusions: ABCG1 mediates oxysterol efflux from oxLDL-loaded macrophages, and the exported oxysterol by ABCG1 pathway can be selectively taken up by hepatocytes. [Copyright &y& Elsevier]

High-density lipoprotein (HDL) plays an important protective role against atherosclerosis, and the anti-atherogenic properties of HDL include the promotion of cellular cholesterol efflux and reverse cholesterol transport (RCT), as well as antioxidant, anti-inflammatory and anticoagulant effects. RCT is a complex pathway, which transports cholesterol from peripheral cells and tissues to the liver for its metabolism and biliary excretion. The major steps in the RCT pathway include the efflux of free cholesterol mediated by cholesterol transporters from cells to the main extracellular acceptor HDL, the conversion of free cholesterol to cholesteryl esters and the subsequent removal of cholesteryl ester in HDL by the liver. The efficiency of RCT is influenced by the mobilization of cellular lipids for efflux and the intravascular remodelling and kinetics of HDL metabolism. Despite the increased cardiovascular risk in people with type 2 diabetes, current knowledge on RCT in diabetes is limited. In this article, abnormalities in RCT in type 2 diabetes mellitus and therapeutic strategies targeting HDL and RCT will be reviewed. [ABSTRACT FROM AUTHOR]

Abstract: In families, well-known monogenic high-density lipoprotein cholesterol (HDL-C) disorders characterized by extreme HDL-C levels on both ends of the continuum occur in multiple HDL pathways and can confer increased risk for atherosclerotic disease. Polygenic HDL-C variants have been more difficult to identify. In many family and twin studies in different populations, HDL-C levels have been shown to be highly heritable, explaining, on average, between 40% and 60% of between-individual variation. This review of abnormal HDL in families addresses known monogenic HDL disorders and HDL-C heritability in the general population, and presents novel data on the heritability of HDL-C in families with a history of premature coronary artery disease. We conclude that levels of HDL-C and HDL abnormalities are largely under genetic control and environmental and behavioral factors alone have only a modest impact. While rare, monogenic disorders offer considerable insight into the genetics of HDL regulation. Moderate to high heritability estimates across different family populations suggest that future genetic studies will be successful in identifying HDL genetic trait loci and that translational studies will ultimately lead to therapies that optimize the cardiovascular protective benefits of HDL. [Copyright &y& Elsevier]

Abstract: Glycogen storage disease type Ia (GSD-Ia) is characterized by hypercholesterolemia, hypertriglyceridemia, decreased cholesterol in high density lipoprotein and increased cholesterol in low and very low density lipoprotein fractions. Despite this pro-atherogenic lipid profile, GSD-Ia patients are not at elevated risk for atherosclerosis. Studies have shown that reverse cholesterol transport and antioxidant capacity can be protective against atherosclerosis. In this study, we show that sera from GSD-Ia patients are more efficient than sera from control subjects in promoting the scavenger receptor class B type I (SR-BI)-mediated cellular cholesterol efflux, a key component in reverse cholesterol transport. The major determinants of the SR-BI-mediated cholesterol efflux are serum phospholipid (PL) and HDL-PL. Phospholipid and that ratio of HDL-PL to HDL are increased in GSD-Ia patients. We further show that sera from GSD-Ia patients have increased total antioxidant capacity compared to controls and this increase correlates with elevated levels of uric acid, a powerful plasma antioxidant. Taken together, the results suggest that the increase in SR-BI-mediated cellular cholesterol efflux and antioxidant capacity in the sera of GSD-Ia patients may contribute to protection against premature atherosclerosis. [Copyright &y& Elsevier]

Abstract: Background: Adipose tissue contains a large amount of cholesterol and performs a buffer function for circulating cholesterol. Scavenger receptor class B type I (SR-BI) might play a significant role in adipocytes cholesterol metabolism through mediation of cholesterol efflux. We evaluated the effect of atorvastatin on SR-BI expression and HDL-induced cholesterol efflux in adipocytes from hypercholesterolemic rabbits. Methods: Sixteen rabbits fed with high-cholesterol diet for 8 weeks were randomly divided into 2 groups: (1) maintained on a high cholesterol diet for 6 weeks (n =8); (2) the same cholesterol diet plus atorvastatin (2.5 mg/kg/day) for 6 weeks (n =8). Control group (n =5) was fed with normal diet for 14 weeks. Subcutaneous adipose was collected for adipocyte culture. Reverse transcription polymerase chain reaction (RT-PCR) was used to evaluate adipocytes SR-BI mRNA expression. Cholesterol efflux rate was determined through measuring release of radioactivity from 3H-cholesterol prelabeled cells into medium containing high-density lipoprotein (HDL). The direct effect of atorvastatin on SR-BI mRNA expression in primary rabbit adipocytes was assayed. Results: High-cholesterol diet decreased SR-BI mRNA expression and reduced HDL-induced cholesterol efflux rate in adipocytes. Six weeks of atorvastatin treatment significantly enhanced the cholesterol efflux from adipocytes, which was related to the increased mRNA expression of SR-BI (r =0.58, P <0.05). Adipocytes SR-BI mRNA expression were negatively correlated with the serum total cholesterol levels at the end of the study (r =−0.46, P <0.05). Atorvastatin dose-dependently stimulated SR-BI mRNA expression in cultured adipocytes. Conclusion: Atorvastatin can up-regulate SR-BI mRNA expression and promote the HDL-induced cholesterol efflux in adipocytes from hypercholesterolemic rabbits possibly through lowering serum cholesterol levels and directly stimulating SR-BI mRNA expression. [Copyright &y& Elsevier]

Abstract: Glycogen storage disease type Ia (GSD-Ia) patients manifest a pro-atherogenic lipid profile but are not at elevated risk for developing atherosclerosis. Serum phospholipid, which correlates positively with the scavenger receptor class B type I (SR-BI)-mediated cholesterol efflux, and apolipoprotein A-IV and E, acceptors for ATP-binding cassette transporter A1 (ABCA1)-mediated cholesterol transport, are increased in GSD-Ia mice. Importantly, sera from GSD-Ia mice are more efficient than sera from control littermates in promoting SR-BI- and ABCA1-mediated cholesterol effluxes. As the first step in reverse cholesterol transport, essential for cholesterol homeostasis, these observations provide one explanation why GSD-Ia patients are apparently protected against premature atherosclerosis. [Copyright &y& Elsevier]

These studies characterized the ontogenesis and regulation of cholesterol turnover in the central nervous system (CNS) of mice. During the first 3 weeks after birth, the CNS grew rapidly and equaled 5% of body weight. The cholesterol pool in this tissue expanded at a rate of 0.26 mg/day and the CNS synthesized sterol at a rate of 0.28 mg/day. In mature mice between 13 and 26 weeks of age, there was a marked decrease in these parameters including a reduction in the relative size of the CNS to 1.7% of body weight, a decrease in the rate of sterol accretion to 0.012 mg/day, and a reduction in the rate of cholesterol synthesis to 0.035 mg/day. Deletion of the NPC1 and CYP46A1 proteins markedly altered cholesterol metabolism in the CNS. However, changes in the plasma cholesterol concentration or loss of function of ATP-binding cassette AI transporter (ABCA1), scavenger receptor class B, type I (SR-BI), low-density lipoprotein receptor (LDLR), APOE or APOAI had no effect on sterol turnover in the brain. Thus, during early development, cholesterol comes entirely from local synthesis. In the adult, however, synthesis exceeds the need for structural cholesterol so that there is a constant excretion of sterol from the CNS into the plasma at a rate of about 0.023 mg/day. [Copyright &y& Elsevier]