High-Density Lipoprotein Functionality as a New Pharmacological Target on Cardiovascular Disease: Unifying Mechanism That Explains High-Density Lipoprotein Protection Toward the Progression of Atherosclerosis.

The formation of the atherosclerotic plaque that is characterized by the accumulation of abnormal amounts of cholesterol-loaded macrophages in the artery wall is mediated by both inflammatory events and alterations of lipid/lipoprotein metabolism. Reverse transport of cholesterol opposes the formation and development of atherosclerotic plaque by promoting high density lipoprotein (HDL)-mediated removal of cholesterol from peripheral macrophages and its delivery back to the liver for excretion into the bile. Although an inverse association between HDL plasma levels and the risk of cardiovascular disease (CVD) has been demonstrated over the years, several studies have recently shown that the antiatherogenic functions of HDL seem to be mediated by their functionality, not always associated with their plasma concentrations. Therefore, assessment of HDL function, evaluated as the capacity to promote cell cholesterol efflux, may offer a better prediction of CVD than HDL levels alone. In agreement with this idea, it has recently been shown that the assessment of serum cholesterol efflux capacity (CEC), as a metric of HDL functionality, may represent a predictor of atherosclerosis extent in humans. The purpose of this narrative review is to summarize the current evidence concerning the role of cholesterol efflux capacity that is important for evaluating CVD risk, focusing on pharmacological evidences and its relationship with inflammation. We conclude that HDL therapeutics are a promising area of investigation but strategies for identifying efficacy must move beyond the idea of simply raising static HDL-cholesterol levels and toward methods of measuring the dynamics of HDL particle remodeling and the generation of lipid-free apolipoprotein A-I (apoA-I). In this way, apoA-I, unlike mature HDL, can promote the greatest extent of cholesterol efflux relieving cellular cholesterol toxicity and the inflammation it causes.

Inhibition of arthritis in the Lewis rat by apolipoprotein A-I and reconstituted high-density lipoproteins.

OBJECTIVE: This study questions whether high-density lipoproteins (HDLs) and apolipoprotein A-I inhibit joint inflammation in streptococcal cell wall peptidoglycan-polysaccharide (PG-PS)-induced arthritis in female Lewis rats. APPROACH AND RESULTS: Administration of PG-PS to female Lewis rats caused acute joint inflammation after 4 days, followed by remission by day 8. The animals subsequently developed chronic joint inflammation that persisted until euthanasia at day 21. Treatment with apolipoprotein A-I 24 hours before and 24 hours after PG-PS administration reduced the acute and chronic joint inflammation. Treatment with apolipoprotein A-I at days 7, 9, and 11 after PG-PS administration reduced the chronic joint inflammation. Treatment with apolipoprotein A-I or reconstituted HDLs consisting of apolipoprotein A-I complexed with phosphatidylcholine 24 hours before and at days 1, 7, 9, and 11 after PG-PS administration reduced acute and chronic joint inflammation. Treatment with apolipoprotein A-I also reduced the inflammatory white blood cell count, synovial fluid proinflammatory cytokine levels, synovial tissue macrophage accumulation, as well as toll-like receptor 2, and inflammatory cytokine expression. At the molecular level, preincubation of human monocyte-derived macrophages with apolipoprotein A-I or reconstituted HDLs before PG-PS stimulation inhibited the PG-PS-induced increase in toll-like receptor 2 and myeloid differentiation primary response gene (88) mRNA levels, nuclear factor-κB activation, and proinflammatory cytokine production. The effects of apolipoprotein A-I and reconstituted HDLs were abolished by transfecting the human monocyte-derived macrophages with ATP-binding cassette transporter A1 or G1 siRNA. CONCLUSIONS: Apolipoprotein A-I and reconstituted HDLs attenuate PG-PS-induced arthritis in the rat. Studies in human monocyte-derived macrophages indicate that this benefit may be because of the inhibition of toll-like receptor 2 expression and decreased nuclear factor-κB activation in macrophages.

Discoidal HDL and apoA-I-derived peptides improve glucose uptake in skeletal muscle.

Lipid-free apoA-I and mature spherical HDL have been shown to induce glucose uptake in skeletal muscle. To exploit apoA-I and HDL states for diabetes therapy, further understanding of interaction between muscle and apoA-I is required. This study has examined whether nascent discoidal HDL, in which apoA-I attains a different conformation from mature HDL and lipid-free states, could induce muscle glucose uptake and whether a specific domain of apoA-I can mediate this effect. Using L6 myotubes stimulated with synthetic reconstituted discoidal HDL (rHDL), we show a glucose uptake effect comparable to insulin. Increased plasma membrane GLUT4 levels in ex vivo rHDL-stimulated myofibers from HA-GLUT4-GFP transgenic mice support this observation. rHDL increased phosphorylation of AMP kinase (AMPK) and acetyl-coA carboxylase (ACC) but not Akt. A survey of domain-specific peptides of apoA-I showed that the lipid-free C-terminal 190-243 fragment increases plasma membrane GLUT4, promotes glucose uptake, and activates AMPK signaling but not Akt. This may be explained by changes in α-helical content of 190-243 fragment versus full-length lipid-free apoA-I as assessed by circular dichroism spectroscopy. Discoidal HDL and the 190-243 peptide of apoA-I are potent agonists of glucose uptake in skeletal muscle, and the C-terminal α-helical content of apoA-I may be an important determinant of this effect.

Scavenger receptor class B type I regulates cellular cholesterol metabolism and cell signaling associated with breast cancer development.

INTRODUCTION: Previous studies have identified cholesterol as an important regulator of breast cancer development. High-density lipoprotein (HDL) and its cellular receptor, the scavenger receptor class B type I (SR-BI) have both been implicated in the regulation of cellular cholesterol homeostasis, but their functions in cancer remain to be established. METHODS: In the present study, we have examined the role of HDL and SR-BI in the regulation of cellular signaling pathways in breast cancer cell lines and in the development of tumor in a mouse xenograft model. RESULTS: Our data show that HDL is capable of stimulating migration and can activate signal transduction pathways in the two human breast cancer cell lines, MDA-MB-231 and MCF7. Furthermore, we also show that knockdown of the HDL receptor, SR-BI, attenuates HDL-induced activation of the phosphatidylinositol 3-kinase (PI3K)/protein Kinase B (Akt) pathway in both cell lines. Additional investigations show that inhibition of the PI3K pathway, but not that of the mitogen-activated protein kinase (MAPK) pathway, could lead to a reduction in cellular proliferation in the absence of SR-BI. Importantly, whereas the knockdown of SR-BI led to decreased proliferation and migration in vitro, it also led to a significant reduction in tumor growth in vivo. Most important, we also show that pharmacological inhibition of SR-BI can attenuate signaling and lead to decreased cellular proliferation in vitro. Taken together, our data indicate that both cholesteryl ester entry via HDL-SR-BI and Akt signaling play an essential role in the regulation of cellular proliferation and migration, and, eventually, tumor growth. CONCLUSIONS: These results identify SR-BI as a potential target for the treatment of breast cancer.

LDL but not HDL increases adiponectin release of primary human adipocytes.

Adipocytes in obesity have inappropriately low cholesterol while adiponectin release is reduced. Cholesterol shortage may contribute to low adiponectin and 3T3-L1 cells treated with lovastatin have diminished adiponectin in cell supernatants. LDL and HDL deliver cholesterol to adipocytes. LDL but not HDL increases adiponectin in cell supernatants of primary human adipocytes. The effect of LDL is not blocked by receptor associated protein suggesting that members of the LDL-receptor family are not involved. To evaluate whether these in vitro observations translate into changes in systemic adiponectin, adiponectin was measured in serum of three patients before, immediately after and 3d after LDL-apheresis. Whereas circulating lipoproteins are reduced immediately after apheresis adiponectin is not changed. Therefore, acute lowering of lipoproteins does not affect systemic adiponectin also excluding that plenty of adiponectin is bound to lipoprotein particles. Accordingly, levels of adiponectin in purified lipoproteins are quite low. Familial hypobetalipoproteinemia (FHBL) is a rare disorder associated with low plasma LDL. Serum adiponectin is, however, similar compared to healthy controls. Thus, neither LDL nor HDL directly contributes to circulating adiponectin concentrations.

[Moxibustion of 45 ℃ at "Zusanli" (ST36) improves vascular endothelial oxidative stress in hyperlipidemia rats].

OBJECTIVE: To explore the antioxidant effect of moxibustion on vascular endothelial function and the under-lying mechanism. METHODS: Forty male SD rats were randomly divided into blank, model, moxibustion and endothelial nitric oxide synthase (eNOS) inhibitor groups, with 10 rats in each group. Hyperlipidemia rat model was established by high fat diet for 8 weeks. Rats in the moxibustion group received 45 ℃ moxibustion at "Zusanli" (ST36) for 10 min once daily for consecutive 4 weeks. Rats in the eNOS inhibitor group received intraperitoneal injection of eNOS inhibitor L-NAME (1 mg/100 g) at the same time of moxibustion intervention. The morphology of abdominal aorta endothelium was observed by HE staining. Lipid deposition in abdominal aorta was observed by oil red O staining. The contents of total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C) in serum and reactive oxygen species (ROS), nitric oxide (NO), superoxide dismutase (SOD), oxidized LDL lipoprotein (ox-LDL), endothelin-1 (ET-1), eNOS, malondialdehyde (MDA) in serum and abdominal aorta were determined by ELISA. The expression of eNOS in abdominal aorta was detected by immunofluorescence. RESULTS: HE staining of the abdominal aorta showed no significant pathological abnormality in the blank group; the endovascular cortex was rough, and the inner, media and outer membrane were rough in the model group; the nucleus and surrounding tissue structure were clear and the vascular wall was smooth in the moxibustion group; abdominal aorta texture was rough in the eNOS inhibitor group. Compared with the blank group, the area of oil red O staining in abdominal aorta increased (P<0.05); the contents of serum TC, TG and LDL-C increased (P<0.01, P<0.05) while HDL-C decreased (P<0.05); the contents of ET-1 in serum and abdominal aorta were increased (P<0.01, P<0.05) while the contents of NO and eNOS were decreased (P<0.05, P<0.001); the contents of ROS, ox-LDL and MDA in serum and abdominal aorta were increased (P<0.001, P<0.01, P<0.000 1) while the content of SOD in abdominal aorta was decreased (P<0.000 1); the expression level of eNOS in abdominal aorta was decreased (P<0.05) in the model group. Compared with the model group, the area of oil red O staining in abdominal aorta decreased (P<0.05); the contents of TC, TG and LDL-C in serum decreased (P<0.05) while HDL-C increased (P<0.05); the contents of ET-1 in serum and abdominal aorta were decreased (P<0.01, P<0.05) while the contents of NO and eNOS in abdominal aorta were increased (P<0.001, P<0.01); the contents of ROS and MDA in serum and abdominal aorta were decreased (P<0.001, P<0.01, P<0.05), the content of ox-LDL was decreased (P<0.01) and the content of SOD was increased (P<0.000 1) in abdominal aorta; the expression level of eNOS in abdominal aorta was increased (P<0.05) in the moxibustion group. Compared with the moxibustion group, the contents of serum TC, LDL-C and MDA in the eNOS inhibitor group were increased (P<0.05); the contents of ET-1, ROS, ox-LDL and MDA in abdominal aorta were increased (P<0.05), the contents of NO, eNOS and SOD were decreased (P<0.05); the expression level of eNOS in abdominal aorta was decreased (P<0.05). CONCLUSION: 45 ℃ moxibustion at ST36 can protect and repair vascular endothelial injury in abdominal aorta of hyperlipidemia rats and improve the oxidative stress of vascular endothelium.

High density lipoprotein cholesterol promotes the proliferation of bone-derived mesenchymal stem cells via binding scavenger receptor-B type I and activation of PI3K/Akt, MAPK/ERK1/2 pathways.

High-density lipoprotein (HDL) possesses protective properties in cardiovascular diseases. However, the effect of HDL on the mesenchymal stem cells (MSCs), which could be mobilized to the damaged myocardial tissue, has not been well elucidated yet. In the current study, we investigated the effect of HDL on the proliferation of MSCs so as to reveal its molecular mechanisms. MSCs derived from rats were treated with HDL in different concentrations and for different periods. The proliferation of MSCs was measured with MTT and BrdU cell proliferation assay. The phosphorylation of Akt, ERK1/2 and the expression of p21 were evaluated by Western blotting. After the activity of respective pathways was down-regulated by the specific inhibitor and the gene of scavenger receptor-B type I (SR-BI) was knocked down by RNA interference, BrdU assay was performed to examine this effect of HDL on MSCs. We found that the proliferation of MSCs induced by HDL, in a time- and concentration-dependent manner, was the phosphorylation of Akt- and ERK1/2-dependent, which was significantly attenuated by the specific inhibitor to respective pathways. Moreover, MAPK/ERK1/2 pathway exerted a more dominating effect on this process. SR-BI contributed to HDL-induced proliferation of MSCs, which was effectively abolished by the silencing of SR-BI. The results suggested that HDL was capable of improving MSCs proliferation, in which MAPK/ERK1/2 and PI3K/Akt pathways involved and SR-BI played a critical role as well.

Monitoring Atheroprotective Macrophage Cholesterol Efflux In Vivo.

This chapter provides details on the methodologies currently used to monitor macrophage cholesterol efflux in vivo in mice. The general principles and techniques described herein can be applied to evaluate the effect of different experimental pathophysiological conditions or the efficacy of different therapeutic strategies on the modulation of in vivo cholesterol efflux to plasma acceptors and the rate of reverse transport of unesterified cholesterol from macrophages to feces in mice.

CETP expression reverses the reconstituted HDL-induced increase in VLDL.

Human data suggest that reconstituted HDL (rHDL) infusion can induce atherosclerosis regression. Studies in mice indicated that rHDL infusion adversely affects VLDL levels, but this effect is less apparent in humans. This discrepancy may be explained by the fact that humans, in contrast to mice, express cholesteryl ester transfer protein (CETP). The aim of this study was to investigate the role of CETP in the effects of rHDL on VLDL metabolism by using APOE*3-Leiden (E3L) mice, a well-established model for human-like lipoprotein metabolism. At 1 h after injection, rHDL increased plasma VLDL-C and TG in E3L mice, but not in E3L mice cross-bred onto a human CETP background (E3L.CETP mice). This initial raise in VLDL, caused by competition between rHDL and VLDL for LPL-mediated TG hydrolysis, was thus prevented by CETP. At 24 h after injection, rHDL caused a second increase in VLDL-C and TG in E3L mice, whereas rHDL had even decreased VLDL in E3L.CETP mice. This secondary raise in VLDL was due to increased hepatic VLDL-TG production. Collectively, we conclude that CETP protects against the rHDL-induced increase in VLDL. We anticipate that studies evaluating the anti-atherosclerotic efficacy of rHDL in mice that are naturally deficient for CETP should be interpreted with caution, and that treatment of atherogenic dyslipidemia by rHDL should not be combined with agents that aggressively reduce CETP activity.

HDL and sphingosine-1-phosphate activate stat3 in prostate cancer DU145 cells via ERK1/2 and S1P receptors, and promote cell migration and invasion.

BACKGROUND: Androgen deprivation therapy in men with prostate cancer leads to a significant increase of high density lipoprotein (HDL), but the effect of HDL on prostate cancer is unknown. Recently, HDL, which transports sphingosine-1-phosphate (S1P), was reported to activate signal transducer and activator of transcription 3 (Stat3) in cardiomyocytes. In this study, we examined the effect of HDL and S1P on Stat3 activation in prostate cancer cells and the involvement of S1P receptors in this process in three prostate cancer cell lines (PC-3, LNCaP, and DU145). METHODS: Discordial reconstituted(r) HDL containing POPC, apoA-1, and S1P were prepared by the cholate dialysis method. The phosphorylations of Stat3, ERK1/2, and Akt were detected by Western blotting. Cell migration and invasion were determined by wound-healing assay and matrigel invasion chamber assay. RESULTS: HDL increased serine 727 phosphorylation of Stat3, but not tyrosine 705 only in DU145 cells. S1P and rHDL-S1P also induced the phosphorylation, but not rHDL without S1P. They also induced DU145 cells migration and invasion. PD98059, a MEK inhibitor, and pertussis toxin, a Gi inhibitor, attenuated HDL-, S1P-, and rHDL-S1P-induced Stat3 phosphorylation, whereas LY294002, a PI3K inhibitor, had no effect. Concerning S1P receptors, S1P1 expression was much lower than S1P2 and S1P3 in DU145 cells. Both JTE013, a S1P2 antagonist, and VPC23019, a S1P1/S1P3 antagonist, attenuated HDL-, S1P-, and rHDL-S1P-induced Stat3 phosphorylations and cell migrations. CONCLUSIONS: These results suggest that the change in HDL plasma levels by androgen deprivation therapy may alter prostate cancer growth and metastasis.

Apolipoprotein A-I stimulates cholesteryl ester transfer protein and apolipoprotein E secretion from lipid-loaded macrophages; the role of NF-κB and PKA signaling pathways.

Cholesteryl ester transfer protein (CETP) and apolipoprotein E (apoE) are secreted by macrophages. Apolipoprotein A-I (apoA-I) is a potent inducer of apoE secretion from lipid-loaded macrophages, but its effect on CETP is not known. We aimed to identify the signaling pathways involved in apoA-I and HDL-mediated regulation of CETP and apoE secretion from lipid-loaded macrophages. THP-1 macrophages were loaded with lipids by incubation with human copper-oxidized LDL. The cells were subsequently exposed to human purified apoA-I or HDL(3) with/without inhibitors of NF-κB (TPCK) or PKA (H89). CETP and apoE in the cultured cells and media were quantified by real-time PCR and Western blot. Results showed that in lipid-loaded macrophages: (i) CETP and apoE gene expression and secretion were increased in the presence of apoA-I, and further increased by inhibition of NF-kB with TPCK; (ii) CETP and apoE gene expression and secretion were reduced by the inhibition of PKA with H89; (iii) PKA-gamma subunit was activated by oxidized LDL and moreover by apoA-I. We also showed that: (i) siRNA-mediated CETP gene silencing diminished apoE secretion from both non-loaded and lipid-loaded macrophages; (ii) addition of apoA-I partially restored apoE secretion from lipid-loaded macrophages with the silenced CETP gene. In conclusion, our data suggest a new mechanism by which apoA-I stimulates CETP secretion, in addition to apoE, from lipid loaded macrophages, a process involving NF-κB inhibition and/or PKA pathway activation.

Anti-Inflammatory HDL Function, Incident Cardiovascular Events, and Mortality: A Secondary Analysis of the JUPITER Randomized Clinical Trial.

Background High-density lipoprotein (HDL) cholesterol has inverse association with cardiovascular disease. HDL possesses anti-inflammatory properties in vitro, but it is unknown whether this may be protective in individuals with inflammation. Methods and Results The functional capacity of HDL to inhibit oxidation of oxidized low-density lipoprotein (ie, the HDL inflammatory index; HII) was measured at baseline and 12 months after random allocation to rosuvastatin or placebo in a nested case-control study of the JUPITER (Justification for the Use of Statins in Prevention: An Intervention Evaluating Rosuvastatin) trial. There were 517 incident cases of cardiovascular disease and all-cause mortality compared to 517 age- and sex-matched controls. Multivariable conditional logistic regression was used to examine associations of HII with events. Median baseline HII was 0.54 (interquartile range, 0.50-0.59). Twelve months of rosuvastatin decreased HII by a mean of 5.3% (95% CI, -8.9% to -1.7%; P=0.005) versus 1.3% (95% CI, -6.5% to 4.0%; P=0.63) with placebo (P=0.22 for between-group difference). HII had a nonlinear relationship with incident events. Compared with the reference group (HII 0.5-1.0) with the lowest event rates, participants with baseline HII ≤0.5 had significantly increased risk of cardiovascular disease/mortality (adjusted hazard ratio, 1.53; 95% CI, 1.06-2.21; P=0.02). Furthermore, there was significant (P=0.002) interaction for HDL particle number with HII, such that having more HDL particles was associated with decreased risk only when HDL was anti-inflammatory. Conclusions In JUPITER participants recruited on the basis of chronic inflammation, HII was associated with incident cardiovascular disease/mortality, with an optimal anti-inflammatory HII range between 0.5 and 1.0. This nonlinear relationship of anti-inflammatory HDL function with risk may account in part for the HDL paradox. Registration URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT00239681.

Transcriptomics Reveal Altered Metabolic and Signaling Pathways in Podocytes Exposed to C16 Ceramide-Enriched Lipoproteins.

Sphingolipids are bioactive lipids associated with cellular membranes and plasma lipoproteins, and their synthesis and degradation are tightly regulated. We have previously determined that low plasma concentrations of certain ceramide species predict the development of nephropathy in diabetes patients with normal albumin excretion rates at baseline. Herein, we tested the hypothesis that altering the sphingolipid content of circulating lipoproteins can alter the metabolic and signaling pathways in podocytes, whose dysfunction leads to an impairment of glomerular filtration. Cultured human podocytes were treated with lipoproteins from healthy subjects enriched in vitro with C16 ceramide, or D-erythro 2-hydroxy C16 ceramide, a ceramide naturally found in skin. The RNA-Seq data demonstrated differential expression of genes regulating sphingolipid metabolism, sphingolipid signaling, and mTOR signaling pathways. A multiplex analysis of mTOR signaling pathway intermediates showed that the majority (eight) of the pathway phosphorylated proteins measured (eleven) were significantly downregulated in response to C16 ceramide-enriched HDL2 compared to HDL2 alone and hydroxy ceramide-enriched HDL2. In contrast, C16 ceramide-enriched HDL3 upregulated the phosphorylation of four intermediates in the mTOR pathway. These findings highlight a possible role for lipoprotein-associated sphingolipids in regulating metabolic and signaling pathways in podocytes and could lead to novel therapeutic targets in glomerular kidney diseases.

Anti-inflammatory therapy with tumour necrosis factor alpha inhibitors improves high-density lipoprotein cholesterol antioxidative capacity in rheumatoid arthritis patients.

OBJECTIVE: High-density lipoprotein (HDL) antiatherogenic functions seem to be diminished during inflammatory conditions such as rheumatoid arthritis (RA). The aim of this study was to investigate the effects of tumour necrosis factor (TNF) inhibition on the antioxidative capacity of HDL in RA. METHODS: Plasma lipids and paraoxonase (PON-1) activity were investigated in 45 RA patients, before and during 6 months of anti-TNF therapy. In addition, HDL was isolated and tested for its ability to inhibit copper-induced oxidation of low-density lipoprotein in vitro. RESULTS: Plasma HDL concentrations did not change considerably after 6 months of therapy. However, stable increases of PON-1 activities were observed throughout the same period (p<0.03). The increases were more obvious when related to HDL or apolipoprotein AI concentrations. HDL total antioxidative capacity significantly improved 6 months after the initiation of anti-TNF therapy (p = 0.015). The initial improvement of PON-1 activity paralleled a decrease in the inflammatory status, whereas specific TNF blockade was likely to be responsible for the long-term effects. CONCLUSIONS: Anti-TNF therapy with infliximab has beneficial effects on lipids through changes in HDL antioxidative capacity, which might be clinically relevant and contribute to the reported protective effect of anti-TNF on cardiovascular morbidity in RA. This emphasises the importance of HDL antiatherogenic capacity for cardiovascular risk in chronic inflammatory conditions.

Biological effects of native and oxidized low-density lipoproteins in cultured human retinal pigment epithelial cells.

Age-related macular degeneration (AMD) and artherosclerosis share common characteristics in their pathogenesis. In this study, we investigated the effects of lipoproteins like native (n)-LDL, oxidized (ox)-LDL and high-density lipoprotein (HDL) on advanced senescence, extracellular matrix accumulation, cell loss, and transforming growth factor-beta2 (TGF-beta2) expression in cultured human retinal pigment epithelial (RPE) cells. Primary human RPE cells were incubated with 10-100 microg/ml n-LDL, ox-LDL, and HDL for 24h. For determination of advanced senescence, beta-galactosidase staining was used. The induction of fibronectin (Fn), laminin alpha 1 (Laa1), and collagen type IV alpha 2 (Col4a2) mRNA was quantified by real-time PCR. Cell loss was investigated by live dead assay. Expression of TGF-beta2 was analyzed by real-time PCR and ELISA assays. Ox-LDL accelerated dose-dependently the onset of RPE senescence, whereas LDL and HDL had no effect. LDL and ox-LDL led to induced expression of Fn, Laa1 and Col4a2, whereas HDL had no influence. Incubation of RPE cells with 100 microg/ml ox-LDL induced marked cell death compared to untreated control cells. Expression of TGF-beta2 was dose-dependently increased by LDL and ox-LDL. LDL and ox-LDL induced cellular changes in RPE cells in vitro, which may resemble pathogenic events of AMD. These results may provide further information about the effects of LDL and ox-LDL in the human RPE and their potential role in the pathogenesis of AMD.

Long pentraxin 3, a key component of innate immunity, is modulated by high-density lipoproteins in endothelial cells.

OBJECTIVE: High-density lipoproteins (HDL) are endowed with cardiovascular protective activities. In addition to their role in reverse cholesterol transport, HDL exert several beneficial effects on endothelial cells, including the induction of endothelial nitric oxide synthase and prostacyclin release, and the control of the immune and inflammatory response. METHODS AND RESULTS: To identify possible mechanisms involved in these effects we investigated the modulation of the expression of acute phase proteins of the pentraxin superfamily, such as C-reactive protein (CRP), serum amyloid P component protein (SAP), and the long pentraxin 3 (PTX3) by HDL in human endothelial cells. HDL induced PTX3 mRNA expression and protein release, whereas no effect was observed on CRP and SAP expression. This effect was mainly dependent on the activation of the lysosphingolipids receptors-PI3K/Akt axis and was mimicked by sphingosine 1 phosphate and other S1P mimetics. This observation was confirmed in vivo; indeed an increased expression of PTX3 mRNA was detected in the aorta of transgenic mice overexpressing human apoA-I, compared to apoA-I knock-out mice. Furthermore, plasma levels of PTX3 significantly increased in C57BL/6 mice injected with HDL. CONCLUSIONS: These data suggest that part of the atheroprotective effects of HDL could result from the modulation of molecules that act as sensors of the immunoinflammatory balance in the vascular wall.

alpha-Tocopherol disturbs macrophage LXRalpha regulation of ABCA1/G1 and cholesterol handling.

Based on the oxidation hypothesis high doses of alpha-tocopherol have been advocated to prevent atherosclerosis, but clinical trials failed to demonstrate a benefit. As specific oxylipids activate PPARgamma and LXRalpha, master regulators of lipid metabolism and cholesterol exporters, we hypothesized, that high dose alpha-tocopherol might interfere with reverse cholesterol transport out of the vessel wall. Human THP-1 cells, a foam cell model, were preincubated with alpha-tocopherol or carrier before exposure to oxidized LDL, delipidated HDL or control buffer. Specific mRNAs were quantified by real-time RT-PCR, LXRalpha activation by a reporter gene assay and cellular cholesterol homeostasis by oxLDL and dHDL facilitated uptake and efflux assays. alpha-Tocopherol significantly reduced baseline expression and stimulation by oxLDL of LXRalpha activity, CD36, ABCA1, and ABCG1. alpha-Tocopherol also reversed the suppression of CD36 and ABCA1 by dHDL. Thus alpha-Tocopherol compromises cellular lipid scavenging and channelling of cholesterol into reverse transport out of the vessel wall.

Cytochrome P450 and gene activation--from pharmacology to cholesterol elimination and regression of atherosclerosis.

BACKGROUND: Lipoproteins are closely associated with the atherosclerotic vascular process. Elevated levels of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein AI (apo AI) in plasma indicate a low probability of coronary heart disease (CHD) together with enhanced longevity, and elevated levels of low-density lipoprotein-cholesterol (LDL-C) and apo B indicate an increased risk of CHD and death. Studies linking gene activation and the induction of cytochrome P450 with elevated plasma levels of apo AI and HDL-C and lowered plasma levels of LDL-C presented a new potential approach to prevent and treat atherosclerotic disease. OBJECTIVE AND METHODS: This is a review aimed at clarifying the effects of P450-enzymes and gene activation on cholesterol homeostasis, the atherosclerotic vascular process, prevention and regression of atherosclerosis and the manifestation of atherosclerotic disease, particularly CHD, the leading cause of death in the world. RESULTS: P450-enzymes maintain cellular cholesterol homeostasis. They respond to cholesterol accumulation by enhancing the generation of hydroxycholesterols (oxysterols) and activating cholesterol-eliminating mechanisms. The CYP7A1, CYP27A1, CYP46A1 and CYP3A4 enzymes generate major oxysterols that enter the circulation. The oxysterols activate-via nuclear receptors-ATP-binding cassette (ABC) A1 and other genes, leading to the elimination of excess cholesterol and protecting arteries from atherosclerosis. Several drugs and nonpharmacologic compounds are ligands for the liver X receptor, pregnane X receptor and other receptors, activate P450 and other genes involved in cholesterol elimination, prevent or regress atherosclerosis and reduce cardiovascular events. CONCLUSIONS: P450-enzymes are essential in the physiological maintenance of cholesterol balance. They activate mechanisms which eliminate excess cholesterol and counteract the atherosclerotic process. Several drugs and nonpharmacologic compounds induce P450 and other genes, prevent or regress atherosclerosis and reduce the occurrence of non-fatal and fatal CHD and other atherosclerotic diseases.

Aerobic exercise training improves the role of high-density lipoprotein antioxidant and reduces plasma lipid peroxidation in type 2 diabetes mellitus.

In this study, we analyzed the effect of aerobic exercise training (AET) and of a single bout of exercise on plasma oxidative stress and on antioxidant defenses in type 2 diabetes mellitus (DM) and in healthy control subjects (C). DM and C did not differ regarding triglycerides, high-density lipoprotein cholesterol (HDL-c), insulin, and HOMA index at baseline and after AET. To measure the lag time for low-density lipoprotein (LDL) oxidation (LAG) and the maximal rate of conjugated diene formation (MCD), participants' plasma HDL(2) and HDL(3) were incubated with LDL from pooled healthy donors' plasma. In the presence of HDL(3), both LAG and MCD were similar in C and DM, but only in DM did AET improve LAG and reduce MCD. In the presence of HDL(2), the lower baseline LAG in DM equaled C after AET. MCD was unchanged in DM after AET, but was lower than C only after AET. Furthermore, after AET plasma thiobarbituric acid-reactive substances were reduced only in DM subjects. Despite not modifying the total plasma antioxidant status and serum paraoxonase-1 activity in both groups, AET lowered the plasma lipid peroxides, corrected the HDL(2), and improved the HDL(3) antioxidant efficiency in DM independent of the changes in blood glucose, insulin, and plasma HDL concentration and composition.