Apo A-I inhibits foam cell formation in Apo E-deficient mice after monocyte adherence to endothelium

Aqueous Humor Apolipoprotein Concentration and Severity of Diabetic Retinopathy in Type 2 Diabetes

An imbalance of plasma apolipoproteins has been linked to diabetic retinopathy (DR); however, there is scarce information regarding their presence in the aqueous humor (AH) and their role in DR. Here, we aimed at analysing the relationship between apolipoprotein concentrations in human AH and the severity of DR. Concentrations of apolipoproteins were measured retrospectively in patients with type 2 diabetes mellitus (T2DM) without DR (n = 23), with mild to moderate nonproliferative DR (NPDR) (n = 13), and advanced NPDR/proliferative DR (PDR) (n = 14) using a multiplex immunoassay. Compared to the non-apparent DR group, the concentrations of seven apolipoproteins were elevated in advanced NPDR/PDR (Apo AI 5.8-fold, Apo AII 4.5-fold, Apo CI 3.3-fold, Apo CIII 6.8-fold, Apo D 3.3-fold, Apo E 2.4-fold, and Apo H 6.6-fold). No significant differences were observed in apolipoprotein concentrations between patients with non-apparent DR and healthy controls (n = 17). In conclusion, the AH concentrations of apolipoproteins AI, AII, CI, CIII, D, E, and H increased in advancing stages of DR, suggesting their role in the pathogenesis of DR, which deserves further examination.

Elevated ApoB/ApoA-I ratio is associated with acute anti-N-Methyl-D-aspartate receptor encephalitis, but not disease outcomes

Objective

The purpose of the present study is to clarify the relationship between the apolipoprotein B100/apolipoprotein A-I (ApoB/ApoA-I) ratio and anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis.

Methods

A total of 71 patients with anti-NMDAR encephalitis were included in this study, and their ApoB/ApoA-I ratios in baseline and follow-up were retrospectively analyzed.

Results

The ApoB/ApoA-I ratio was closely correlated with the baseline-modified Rankin scale (mRS) score of >3 in patients with anti-NMDAR encephalitis. A subgroup analysis showed obvious differences between the high and low ApoB/ApoA-I ratio groups. The ApoB/ApoA-I ratio was positively correlated with intensive care unit (ICU) treatment, length of hospital stay, baseline mRS score, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR). The ratios of the high and low ApoB/ApoA-I groups both improved in the follow-up.

Conclusion

The increased ApoB/ApoA-I ratio is associated with acute anti-NMDAR encephalitis, but not disease outcomes. Serum ApoB/ApoA-I ratio was related to inflammation and immunity in peripheral blood. The findings might provide a new idea for further exploration of the pathogenesis and treatment of anti-NMDAR encephalitis.

Lack of ApoA-I in ApoEKO Mice Causes Skin Xanthomas, Worsening of Inflammation, and Increased Coronary Atherosclerosis in the Absence of Hyperlipidemia

Background:

HDL (high-density lipoprotein) and its major protein component, apoA-I (apolipoprotein A-I), play a unique role in cholesterol homeostasis and immunity. ApoA-I deficiency in hyperlipidemic, atheroprone mice was shown to drive cholesterol accumulation and inflammatory cell activation/proliferation. The present study was aimed at investigating the impact of apoA-I deficiency on lipid deposition and local/systemic inflammation in normolipidemic conditions.

Methods:

ApoE deficient mice, apoE/apoA-I double deficient (DKO) mice, DKO mice overexpressing human apoA-I, and C57Bl/6J control mice were fed normal laboratory diet until 30 weeks of age. Plasma lipids were quantified, atherosclerosis development at the aortic sinus and coronary arteries was measured, skin ultrastructure was evaluated by electron microscopy. Blood and lymphoid organs were characterized through histological, immunocytofluorimetric, and whole transcriptome analyses.

Results:

DKO were characterized by almost complete HDL deficiency and by plasma total cholesterol levels comparable to control mice. Only DKO showed xanthoma formation and severe inflammation in the skin-draining lymph nodes, whose transcriptome analysis revealed a dramatic impairment in energy metabolism and fatty acid oxidation pathways. An increased presence of CD4⁺ T effector memory cells was detected in blood, spleen, and skin-draining lymph nodes of DKO. A worsening of atherosclerosis at the aortic sinus and coronary arteries was also observed in DKO versus apoE deficient. Human apoA-I overexpression in the DKO background was able to rescue the skin phenotype and halt atherosclerosis development.

Conclusions:

HDL deficiency, in the absence of hyperlipidemia, is associated with severe alterations of skin morphology, aortic and coronary atherosclerosis, local and systemic inflammation.

Low apoA-I is associated with insulin resistance in patients with impaired glucose tolerance: a cross-sectional study

Background

Low apolipoprotein A-I (apoA-I) is an independent risk factor for atherosclerotic cardiovascular diseases. Insulin resistance predicts the progression of abnormal glucose metabolism, which is the main cause of atherosclerotic cardiovascular disease. In this study, we assessed the potential association between apoA-I levels and insulin resistance in patients with impaired glucose tolerance (IGT) and the possible link between apoA-I and IGT.

Methods

This study evaluated a cross-sectional study of 108 participants with impaired glucose tolerance (IGT group) and 84 controls (control group). ApoA-I and clinical characteristics were measured, and a homeostasis model assessment of insulin resistance (HOMA-IR) was calculated.

Results

The IGT group exhibited significantly lower apoA-I and higher HOMA-IR levels than the control group (apoA-I: 1.37 ± 0.36 vs 1.57 ± 0.39 g/L; HOMA-IR: 4.21 ± 1.56 vs 2.15 ± 0.99; P < 0.001 for both). ApoA-I was negatively correlated with HOMA-IR in both the IGT and control groups (IGT group: r = −0.269, P = 0.005; control group: r = −0.262, P = 0.016). Multiple stepwise regression analysis showed that low apoA-I levels (β = −1.470, P = 0.002) were independently correlated with high HOMA-IR levels in the IGT group. Moreover, logistic regression analysis identified that low apoA-I was an independent influencing factor for IGT (β = −1.170, OR = 0.310, P = 0.007).

Conclusions

ApoA-I is inversely associated with insulin resistance in patients with impaired glucose tolerance, and low apoA-I is an independent risk factor for impaired glucose tolerance. These results indicate that apoA-I plays an important role in regulating insulin sensitivity and glucose metabolism in patients with IGT.

Deficiency of ATP-Binding Cassette Transporters A1 and G1 in Endothelial Cells Accelerates Atherosclerosis in Mice

OBJECTIVE

Plasma high-density lipoproteins have several putative antiatherogenic effects, including preservation of endothelial functions. This is thought to be mediated, in part, by the ability of high-density lipoproteins to promote cholesterol efflux from endothelial cells (ECs). The ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1) interact with high-density lipoproteins to promote cholesterol efflux from ECs. To determine the impact of endothelial cholesterol efflux pathways on atherogenesis, we prepared mice with endothelium-specific knockout of Abca1 and Abcg1.

APPROACH AND RESULTS

Generation of mice with EC-ABCA1 and ABCG1 deficiency required crossbreeding Abca1(fl/fl)Abcg1(fl/fl)Ldlr(-/-) mice with the Tie2Cre strain, followed by irradiation and transplantation of Abca1(fl/fl)Abcg1(fl/fl) bone marrow to abrogate the effects of macrophage ABCA1 and ABCG1 deficiency induced by Tie2Cre. After 20 to 22 weeks of Western-type diet, both single EC-Abca1 and Abcg1 deficiency increased atherosclerosis in the aortic root and whole aorta. Combined EC-Abca1/g1 deficiency caused a significant further increase in lesion area at both sites. EC-Abca1/g1 deficiency dramatically enhanced macrophage lipid accumulation in the branches of the aorta that are exposed to disturbed blood flow, decreased aortic endothelial NO synthase activity, and increased monocyte infiltration into the atherosclerotic plaque. Abca1/g1 deficiency enhanced lipopolysaccharide-induced inflammatory gene expression in mouse aortic ECs, which was recapitulated by ABCG1 deficiency in human aortic ECs.

CONCLUSIONS

These studies provide direct evidence that endothelial cholesterol efflux pathways mediated by ABCA1 and ABCG1 are nonredundant and atheroprotective, reflecting preservation of endothelial NO synthase activity and suppression of endothelial inflammation, especially in regions of disturbed arterial blood flow.

Hyperhomocysteinemia is associated with decreased apolipoprotein AI levels in normal healthy people

Background

Hyperhomocysteinemia (HHcy) is an independent risk factor for various cardiovascular diseases. Animal studies have shown that homocysteine (Hcy) inhibits hepatic expression of apolipoprotein AI (apoAI). Our recent clinical study showed that increased plasma Hcy levels were associated with decreased apoAI levels in patients with impaired glucose tolerance. In this study, we assessed a potential association between Hcy and apoAI levels in normal healthy people.

Methods

A total of 1768 normal healthy individuals were divided into two groups: the control group (subjects without HHcy) and the HHcy group (subjects with HHcy).

Results

HHcy subjects exhibited significantly lower high-density lipoprotein cholesterol (HDL-C) and apoAI levels than the control group (HDL-C: 1.18 ± 0.25 vs. 1.29 ± 0.32 mmol/L; apoAI: 1.38 ± 0.19 vs. 1.47 ± 0.25 g/L; all P < 0.01). Plasma Hcy levels were negatively associated with HDL-C and apoAI levels after adjustments for age, BMI and TG (HDL-C: r = –0.10; apoAI: r = –0.11; all P < 0.05). Multivariate regression analysis showed that the plasma Hcy levels were an independent influencing factor for apoAI (β = –0.065, P < 0.05).

Conclusions

Increased plasma Hcy levels were associated with decreased apoAI levels in normal healthy people, and the inhibition of apoAI synthesis might be a mechanism through which Hcy is linked with the development of atherosclerosis in HHcy subjects.

Dysfunctional HDL: from structure-function-relationships to biomarkers

Reduced plasma levels of HDL-C are associated with an increased risk of CAD and myocardial infarction, as shown in various prospective population studies. However, recent clinical trials on lipid-modifying drugs that increase plasma levels of HDL-C have not shown significant clinical benefit. Notably, in some recent clinical studies, there is no clear association of higher HDL-C levels with a reduced risk of cardiovascular events observed in patients with existing CAD. These observations have prompted researchers to shift from a cholesterol-centric view of HDL towards assessing the function and composition of HDL particles. Of importance, experimental and translational studies have further demonstrated various potential antiatherogenic effects of HDL. HDL has been proposed to promote macrophage reverse cholesterol transport and to protect endothelial cell functions by prevention of oxidation of LDL and its adverse endothelial effects. Furthermore, HDL from healthy subjects can directly stimulate endothelial cell production of nitric oxide and exert anti-inflammatory and antiapoptotic effects. Of note, increasing evidence suggests that the vascular effects of HDL can be highly heterogeneous and HDL may lose important anti-atherosclerotic properties and turn dysfunctional in patients with chronic inflammatory disorders. A greater understanding of mechanisms of action of HDL and its altered vascular effects is therefore critical within the context of HDL-targeted therapies.

High-density lipoprotein and atherosclerosis regression: evidence from preclinical and clinical studies

High-density lipoprotein (HDL) particles transport (among other molecules) cholesterol (HDL-C). In epidemiological studies, plasma HDL-C levels have an inverse relationship to the risk of atherosclerotic cardiovascular disease. It has been assumed that this reflects the protective functions of HDL, which include their ability to promote cholesterol efflux. Yet, several recent pharmacological and genetic studies have failed to demonstrate that increased plasma levels of HDL-C resulted in decreased cardiovascular disease risk, giving rise to a controversy regarding whether plasma levels of HDL-C reflect HDL function, or that HDL is even as protective as assumed. The evidence from preclinical and (limited) clinical studies shows that HDL can promote the regression of atherosclerosis when the levels of functional particles are increased from endogenous or exogenous sources. The data show that regression results from a combination of reduced plaque lipid and macrophage contents, as well as from a reduction in its inflammatory state. Although more research will be needed regarding basic mechanisms and to establish that these changes translate clinically to reduced cardiovascular disease events, that HDL can regress plaques suggests that the recent trial failures do not eliminate HDL from consideration as an atheroprotective agent but rather emphasizes the important distinction between HDL function and plasma levels of HDL-C.

In vivo fluorescence-mediated tomography imaging demonstrates atorvastatin-mediated reduction of lesion macrophages in ApoE-/- mice

BACKGROUND

Macrophage recruitment into atherosclerotic plaques drives lesion progression, destabilization, and rupture. Chronic statin treatment reduces macrophage plaque content. Information on dynamics of macrophage recruitment would help assessing plaque vulnerability and guiding therapy. Techniques to image macrophage homing to vulnerable plaques in vivo are scarcely available. The authors tested if noninvasive fluorescence-mediated tomography (FMT) can assess plaque-stabilizing effects of short-term high-dosage atorvastatin.

METHODS

Macrophages from green-fluorescent-protein-transgenic mice were labeled with a near-infrared fluorescent dye and were injected IV in apolipoprotein E-deficient mice (n=9) on Western diet 7 days after guidewire-injury of the carotid artery. FMT-scans, 2 and 7 days thereafter, quantified macrophage recruitment into carotid artery plaques. Atorvastatin was tested for macrophage adhesion, proliferation, and viability (n=5 to 6) in vitro. Fourteen mice received atorvastatin or vehicle for 4 days after 16 weeks on Western diet. FMT assessed macrophage recruitment into aortic and innominate artery lesions. Means (±SD)% are reported.

RESULTS

Double-labeled macrophages were recruited into carotid artery lesions. FMT resolved fluorescence projecting on the injured carotid artery and detected a signal increase to 300% (±191) after guidewire injury. Atorvastatin reduced macrophage adhesion to activated endothelial cells by 36% (±19). In a clinically relevant proof-of-concept intervention, FMT-imaging detected that 4 days atorvastatin treatment reduced macrophage recruitment by 57% (±8) indicating plaque stabilization. Immunohistochemistry confirmed reduced macrophage infiltration.

CONCLUSIONS

FMT optical imaging proved its high potential for clinical applicability for tracking recruitment of near-infrared fluorescent-labeled macrophages to vulnerable plaques in vivo. FMT-based quantification of macrophage recruitment demonstrated rapid plaque stabilization by 4-day atorvastatin treatment in apolipoprotein E-deficient mice.

High density lipoproteins and endothelial functions: mechanistic insights and alterations in cardiovascular disease

Prospective population studies in the primary prevention setting have shown that reduced plasma levels of HDL cholesterol are associated with an increased risk of coronary disease and myocardial infarction. Experimental and translational studies have further revealed several potential anti-atherogenic effects of HDL, including protective effects on endothelial cell functions. HDL has been suggested to protect endothelial cell functions by prevention of oxidation of LDL and its adverse endothelial effects. Moreover, HDL from healthy subjects can directly stimulate endothelial cell production of nitric oxide and anti-inflammatory, anti-apoptotic, and anti-thrombotic effects as well as endothelial repair processes. However, several recent clinical trials using HDL cholesterol-raising agents, such as torcetrapib, dalcetrapib, and niacin, did not demonstrate a significant reduction of cardiovascular events in patients with coronary disease. Of note, growing evidence suggests that the vascular effects of HDL can be highly heterogeneous and vasoprotective properties of HDL are altered in patients with coronary disease. Characterization of underlying mechanisms and understanding of the clinical relevance of this "HDL dysfunction" is currently an active field of cardiovascular research. Notably, in some recent studies no clear association of higher HDL cholesterol levels with a reduced risk of cardiovascular events was observed in patients with already established coronary disease. A greater understanding of mechanisms of action of HDL and its altered vascular effects is therefore critical within the context of HDL-targeted therapies. In this review, we will address different effects of HDL on endothelial cell functions potentially relevant to atherosclerotic vascular disease and explore molecular mechanisms leading to "dysfunctional HDL".

Deficiency of ATP-binding cassette transporters A1 and G1 in macrophages increases inflammation and accelerates atherosclerosis in mice

RATIONALE

Plasma high-density lipoprotein levels are inversely correlated with atherosclerosis. Although it is widely assumed that this is attributable to the ability of high-density lipoprotein to promote cholesterol efflux from macrophage foam cells, direct experimental support for this hypothesis is lacking.

OBJECTIVE

To assess the role of macrophage cholesterol efflux pathways in atherogenesis.

METHODS AND RESULTS

We developed mice with efficient deletion of the ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1) in macrophages (MAC-ABC(DKO) mice) but not in hematopoietic stem or progenitor populations. MAC-ABC(DKO) bone marrow (BM) was transplanted into Ldlr(-/-) recipients. On the chow diet, these mice had similar plasma cholesterol and blood monocyte levels but increased atherosclerosis compared with controls. On the Western-type diet, MAC-ABC(DKO) BM-transplanted Ldlr(-/-) mice had disproportionate atherosclerosis, considering they also had lower very low-density lipoprotein/low-density lipoprotein cholesterol levels than controls. ABCA1/G1-deficient macrophages in lesions showed increased inflammatory gene expression. Unexpectedly, Western-type diet-fed MAC-ABC(DKO) BM-transplanted Ldlr(-/-) mice displayed monocytosis and neutrophilia in the absence of hematopoietic stem and multipotential progenitor cells proliferation. Mechanistic studies revealed increased expressions of machrophage colony stimulating factor and granulocyte colony stimulating factor in splenic macrophage foam cells, driving BM monocyte and neutrophil production.

CONCLUSIONS

These studies show that macrophage deficiency of ABCA1/G1 is proatherogenic likely by promoting plaque inflammation and uncover a novel positive feedback loop in which cholesterol-laden splenic macrophages signal BM progenitors to produce monocytes, with suppression by macrophage cholesterol efflux pathways.

High-density lipoprotein loses its anti-inflammatory capacity by accumulation of pro-inflammatory-serum amyloid A

AIMS

High-density lipoprotein (HDL) is known to have potent anti-inflammatory properties. Monocyte chemoattractant protein-1 is an important pro-inflammatory cytokine in early atherogenesis. There is evidence that HDL can lose its protective function during inflammatory disease. In patients with end-stage renal disease (ESRD), epidemiological studies have documented that the inverse correlation between HDL-cholesterol and cardiovascular risk is lost. Many structural modifications leading to reduced HDL function have been characterized, but the functional consequences are not fully understood.

METHODS AND RESULTS

We showed that HDL from patients with ESRD has a lower anti-inflammatory potential by reduced inhibition of monocyte chemoattractant protein-1 formation in vascular smooth muscle cells. Via a proteomic approach, we identified proteins in HDL from ESRD patients exerting pro-inflammatory actions. By chromatographic separation of proteins and mass-spectrometric analysis, we found serum amyloid A (SAA) to be one molecule acting as a potent pro-inflammatory protein. SAA is enriched in HDL from ESRD patients, correlating with reduced anti-inflammatory capacity. In SAA signal transduction, activation of formyl-peptide receptor 2 is involved. SAA enrichment in HDL of healthy subjects reduced the anti-inflammatory capacity of HDL and correlated with its decreased function.

CONCLUSION

These results suggest that SAA enrichment of HDL during disease conditions contributes to the decreased protective function. It is a novel finding that SAA acts as a pro-inflammatory molecule to reduce the anti-inflammatory properties of HDL.

Hyperglycemia in apolipoprotein E-deficient mouse strains with different atherosclerosis susceptibility

Background

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of atherosclerotic vascular disease, but it is unknown whether the other way around is true too. C57BL/6 (B6) and BALB/cJ (BALB) are two mouse strains that differ markedly in their susceptibility to atherosclerosis. In this study we investigated the development of diet-induced T2DM in these two strains.

Methods and Results

When deficient in apolipoprotein E (apoE^-/-) and fed a Western diet for 12 weeks, atherosclerosis-susceptible B6 mice developed significant hyperglycemia. In contrast, atherosclerosis-resistant BALB apoE^-/- mice had much lower plasma glucose levels than B6.apoE^-/- mice on either chow or Western diet and during an intraperitoneal glucose tolerance test. In response to glucose BALB.apoE^-/- mice displayed both the first and second phases of insulin secretion but the second phase of insulin secretion was absent in B6.apoE^-/- mice. In response to insulin B6.apoE^-/- mice showed a deeper and longer-lasting fall in blood glucose levels while BALB.apoE^-/- mice showed little reduction in glucose levels. Pancreatic islet area of BALB.apoE^-/- mice on light microscopy nearly doubled the area of B6.apoE^-/- mice. Most circulating proinflammatory cytokines were lower in BALB.apoE^-/- than in B6.apoE^-/- mice on the Western diet, as determined by protein arrays. Increased macrophage infiltration in islets was observed in B6.apoE^-/- mice by immunostaining for Mac2 and also by flow cytometry.

Conclusion

This study demonstrates that defects in insulin secretion rather than defects in insulin resistance explain the marketed difference in susceptibility to T2DM in the B6.apoE^-/- and BALB.apoE^-/- mouse model. A smaller islet mass and more prominent islet inflammation may explain the vulnerability of B6.apoE^-/- mice to diet-induced diabetes.

Modulation of vitamin D signaling is a potential therapeutic target to lower cardiovascular risk in chronic kidney disease

While it is true that many traditional cardiovascular risk factors are amenable to intervention in chronic kidney disease (CKD), the results of intervention may not be as efficacious as those obtained in the general population. Thus, there may also be a unique milieu established in CKD, which causes excess cardiovascular disease (CVD) burden by mechanisms that are as yet not fully recognized. Recently, vitamin D has sparked widespread interest because of its potential favorable benefits on CVD. However, the mechanisms for how vitamin D may improve CVD risk markers and outcomes have not been fully elucidated. Furthermore, hypovitaminosis D is highly prevalent in the CKD cohort. Given this background, we hypothesize that low vitamin D status may act as a new CVD risk marker, and modulation of vitamin D signaling may be a potential therapeutic target to lower cardiovascular risk in CKD. The data presented in this review support that the low vitamin D status may be linked with the high cardiovascular risk in CKD, based on both the biological effects of vitamin D itself on the cardiovascular system, and the cross-actions between vitamin D signaling and the multiple metabolic pathways. Considering the high prevalence of hypovitaminosis D, limited natural vitamin D food sources, and reduced sun exposure in CKD patients, recommendations for treatment of hypovitaminosis D mainly focus on exogenous supplementation with vitamin D and its analogues. Although promising, when to start therapy, the route of administration, the dose, and the duration remain need to be discussed.

Anti-atherogenic mechanisms of high density lipoprotein: effects on myeloid cells

In some settings increasing high density lipoprotein (HDL) levels has been associated with a reduction in experimental atherosclerosis. This has been most clearly seen in apolipoprotein A-I (apoA-I) transgenic mice or in animals infused with HDL or its apolipoproteins. A major mechanism by which these treatments are thought to delay progression or cause regression of atherosclerosis is by promoting efflux of cholesterol from macrophage foam cells. In addition, HDL has been described as having anti-inflammatory and other beneficial effects. Some recent research has linked anti-inflammatory effects to cholesterol efflux pathways but likely multiple mechanisms are involved. Macrophage cholesterol efflux may have a role in facilitating emigration of macrophages from lesions during regression. While macrophages can mediate cholesterol efflux by several pathways, studies in knockout mice or cells point to the importance of active efflux mediated by ATP binding cassette transporter (ABC) A1 and G1. In addition to traditional roles in macrophages, these transporters have been implicated in the control of hematopoietic stem cell proliferation, monocytosis and neutrophilia, as well as activation of monocytes and neutrophils. Thus, HDL and cholesterol efflux pathways may have important anti-atherogenic effects at all stages of the myeloid cell/monocyte/dendritic cell/macrophage lifecycle. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Tannic acid is more effective than clofibrate for the elevation of hepatic β-oxidation and the inhibition of 3-hydroxy-3-methyl-glutaryl-CoA reductase and aortic lesion formation in apo E-deficient mice

The effects of tannic acid (TA) supplementation (0·02 %, wt/wt) were compared with the effects of clofibrate (CF) supplementation (0·02 %, wt/wt) in apo E-deficient (apo E(- / -)) mice fed a AIN-76 semi-synthetic diet (normal diet) over 20 weeks. The mice were monitored for the modulation of hepatic mRNA expression and the activities of lipid-regulating enzymes. Both TA and CF supplementation lowered hepatic 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR) activity and prevented atherosclerotic lesion formation in comparison with the control group. Hepatic carnitine palmitoyl transferase and β-oxidation activities were significantly higher in the TA and CF groups than in the control group. Both CF and TA supplementation resulted in significant decreases in hepatic HMGR mRNA levels in association with its enzyme activity. However, in contrast to CF supplementation, TA supplementation seemed to decrease the accumulation of hepatic lipids in the apo E(- / -) mice without increasing liver weight. These results suggest that the overall effect of TA is more desirable than CF for the alleviation of hepatic lipogenesis and atherogenesis in apo E(- / -) mice.

Neutrophil activation is attenuated by high-density lipoprotein and apolipoprotein A-I in in vitro and in vivo models of inflammation

OBJECTIVE

Neutrophils play a key role in the immune response but can undesirably exacerbate inflammation. High-density lipoproteins (HDL) are antiinflammatory particles, exerting beneficial cardiovascular influences. We determined whether HDL exerts antiinflammatory effects on neutrophils and explored the mechanisms by which these occur.

METHODS AND RESULTS

CD11b on activated human neutrophils was significantly attenuated by apolipoprotein A-I (apoA-I) and HDL. The effects of apoA-I were mediated via ABCA1, whereas the effects of HDL were via scavenger receptor BI. Both were associated with a reduction in the abundance of lipid rafts, and a strong correlation between raft abundance and CD11b activation was observed. ApoA-I and HDL reduced neutrophil adhesion to a platelet monolayer under shear flow, as well as neutrophil spreading and migration. ApoA-I also inhibited leukocyte recruitment to the endothelium in an acute in vivo model of inflammation. Finally, infusion of reconstituted HDL in patients with peripheral vascular disease was demonstrated to significantly attenuate neutrophil activation.

CONCLUSION

We describe here a novel role for HDL and apoA-I in regulating neutrophil activation using in vitro, in vivo, and clinical approaches. We also show that these effects of HDL and apoA-I involve a mechanism requiring changes in membrane domain content rather than in cholesterol efflux per se.

High-density lipoprotein metabolism and endothelial function

PURPOSE OF REVIEW

High-density lipoprotein (HDL) protects against atherosclerosis, transporting cholesterol from peripheral cells to the liver, where it is excreted into the bile. However, HDL also has prominent vascular protective effects.

RECENT FINDINGS

Recent studies have uncovered mechanisms through which HDL decreases vascular inflammation, boosts nitric oxide production, and inhibits thrombosis. The discovery that dysfunctional HDL can also have proinflammatory effects has uncovered a new aspect of HDL biology.

SUMMARY

Low-density lipoprotein is the primary target for drug therapy of dyslipidemias. Drugs that increase HDL also affect additional metabolic pathways. Development of selective drugs targeting key aspects of HDL metabolism may enable us to alter the composition of HDL and inhibit atherogenesis.

Infiltration of macrophages through the atrial endocardium of inflammation-induced rats: contribution of fractalkine

BACKGROUND

Inflammatory processes in the atria during systemic inflammation remain unclear, so this study tested the hypothesis that macrophages infiltrate the atrial myocardium mainly through the atrial endocardium with the contribution of fractalkine.

METHODS AND RESULTS

Sprague-Dawley rats were injected with lipopolysaccharide (LPS) to simulate inflammation in the atria. Inflammation was immunohistologically assessed by the presence of macrophages. Macrophage infiltration was diffuse throughout the atrial myocardium after LPS injection. At an earlier phase after LPS injection, the number of macrophages dramatically increased, mainly in the atrial endocardium, and the expression of fractalkine protein was markedly increased by treatment with LPS in the atrial endocardium. The LPS-induced increase in atrial macrophage infiltration was significantly suppressed by neutralizing the fractalkine protein (P<0.01).

CONCLUSIONS

In an experimental model of atrial inflammation, macrophages infiltrated the myocardium mainly through the atrial endocardium with the contribution of fractalkine. Inhibition of macrophage infiltration by suppressing chemokine expression could be a novel therapeutic approach to controling acute inflammation in the atria.

High-density lipoproteins, inflammation and oxidative stress

Plasma levels of HDL (high-density lipoprotein)-cholesterol are strongly and inversely correlated with atherosclerotic cardiovascular disease. Both clinical and epidemiological studies have reported an inverse and independent association between serum HDL-cholesterol levels and CHD (coronary heart disease) risk. The cardioprotective effects of HDLs have been attributed to several mechanisms, including their involvement in the reverse cholesterol transport pathway. HDLs also have antioxidant, anti-inflammatory and antithrombotic properties and promote endothelial repair, all of which are likely to contribute to their ability to prevent CHD. The first part of this review summarizes what is known about the origins and metabolism of HDL. We then focus on the anti-inflammatory and antioxidant properties of HDL and discuss why these characteristics are cardioprotective.

Squalene in a sex-dependent manner modulates atherosclerotic lesion which correlates with hepatic fat content in apoE-knockout male mice

BACKGROUND

Squalene is an intermediate of cholesterol biosynthesis which can be obtained from the diet where it is abundant, for example, in olive oil. The effect of this isoprenoid on the development of atherosclerosis was investigated on apoE-knockout mice.

METHODS AND RESULTS

Two groups of animals, separated according to sex, were fed on standard chow diet: the control group receiving only vehicle and the second group an aqueous solution of squalene to provide a dose of 1g/kg/day in male and female mice. This treatment was maintained for 10 weeks. At the end of this period, plasma lipid parameters, oxidative stress markers and hepatic fat were measured as well as cross-sectional lesion area of aortic root in both groups. Data showed that in males squalene feeding reduced atherosclerotic lesion area independently of plasma lipids and activation of circulating monocytes. In contrast, squalene intake did not decrease lesion area in females, despite reducing plasma cholesterol and triglycerides, isoprostane and percentage of Mac-1 expressing white cells. In males, atherosclerotic lesion area was positively and significantly associated with hepatic fat content and the plasma triglycerides were also strongly associated with liver weight.

CONCLUSIONS

These results indicate that administration of squalene modulates lesion development in a gender specific manner, and that accumulation of hepatic fat by liver is highly correlated with lesion progression in males. Hence, squalene administration could be used as a safe alternative to correct hepatic steatosis and atherosclerosis particularly in males.

Cholesterol efflux pathways and other potential mechanisms involved in the athero-protective effect of high density lipoproteins

Plasma high density lipoprotein (HDL) levels bear a strong independent inverse relationship with atherosclerotic cardiovascular disease. Although HDL has anti-oxidant, anti-inflammatory, vasodilating and anti-thrombotic properties, the central anti-atherogenic activity of HDL is likely to be its ability to remove cholesterol and oxysterols from macrophage foam cells, smooth muscle cells and endothelial cells in the arterial wall. To some extent, the pleotropic athero-protective properties of HDL may be related to its ability to promote sterol and oxysterol efflux from arterial wall cells, as well as to detoxify oxidized phospholipids. In cholesterol-loaded macrophages, activation of liver X receptors (LXRs) leads to increased expression of adenosine triphosphate (ATP) binding cassetter transporter (ABCA1), ATP binding cassetter transporter gene (ABCG1) and apoE and promotes cholesterol efflux. ABCA1 stimulates cholesterol efflux to lipid-poor apolipoproteins, whilst ABCG1 promotes efflux of cholesterol and oxysterols to HDL. Despite some recent setbacks in the clinical arena, there is still intense interest in therapeutically targeting HDL and macrophage cholesterol efflux pathways, via treatments with niacin, cholesterol ester transfer protein inhibitors, LXR activators and infusions of apoA-1, phospholipids and peptides.

Continuous intake of polyphenolic compounds containing cocoa powder reduces LDL oxidative susceptibility and has beneficial effects on plasma HDL-cholesterol concentrations in humans

BACKGROUND

Cocoa powder is rich in polyphenols such as catechins and procyanidins and has been shown in various models to inhibit LDL oxidation and atherogenesis.

OBJECTIVE

We examined whether long-term intake of cocoa powder alters plasma lipid profiles in normocholesterolemic and mildly hypercholesterolemic human subjects.

DESIGN

Twenty-five subjects were randomly assigned to ingest either 12 g sugar/d (control group) or 26 g cocoa powder and 12 g sugar/d (cocoa group) for 12 wk. Blood samples were collected before the study and 12 wk after intake of the test drinks. Plasma lipids, LDL oxidative susceptibility, and urinary oxidative stress markers were measured.

RESULTS

At 12 wk, we measured a 9% prolongation from baseline levels in the lag time of LDL oxidation in the cocoa group. This prolongation in the cocoa group was significantly greater than the reduction measured in the control group (-13%). A significantly greater increase in plasma HDL cholesterol (24%) was observed in the cocoa group than in the control group (5%). A negative correlation was observed between plasma concentrations of HDL cholesterol and oxidized LDL. At 12 wk, there was a 24% reduction in dityrosine from baseline concentrations in the cocoa group. This reduction in the cocoa group was significantly greater than the reduction in the control group (-1%).

CONCLUSION

It is possible that increases in HDL-cholesterol concentrations may contribute to the suppression of LDL oxidation and that polyphenolic substances derived from cocoa powder may contribute to an elevation in HDL cholesterol.

Piperine, an active principle from Piper nigrum, modulates hormonal and apo lipoprotein profiles in hyperlipidemic rats

PURPOSE

To study the effect of piperine, an alkaloid, on thyroid hormones and apolipoproteins in high-fat-diet (HFD) and antithyroid drug-induced hyperlipidemic rats.

EXPERIMENTAL

Male Wistar rats were first divided into two groups, control diet and high-fat diet (HFD) and then subdivided into four subgroups of ten animals each. The animals were treated with the following regimens for 10 weeks: 1% carboxymethyl cellulose; 10 mg carbimazole (CM)/kg body weight; 10 mg CM + 40 mg piperine/kg body weight, and 10 mg CM + 2 mg atorvastatin /ATV//kg body weight. Lipid profiles, hormone levels, and apolipoprotein levels were studied in all groups.

RESULTS

HFD and/or CM administration significantly elevated the plasma levels of total cholesterol, VLDL, LDL, triglycerides, free fatty acids, and phospholipids, but significantly reduced the HDL levels. Moreover, CM administration significantly reduced apo A-I levels and T3, T4 and testosterone levels while significantly elevating plasma apo B, thyroid stimulating hormone (TSH) and insulin levels. The simultaneous administration of piperine and HFD significantly reduced plasma lipids and lipoproteins levels, except for HDL, which was significantly elevated. Piperine supplementation also improved the plasma levels of apo A-I, T3, T4, testosterone, and I and significantly reduced apo B, TSH, and insulin to near normal levels.

CONCLUSIONS

The data presented here provide evidence that piperine possesses thyrogenic activity, thus modulating apolipoprotein levels and insulin resistance in HFD-fed rats, opening a new view in the management of dyslipidemia by dietary supplementation with nutrients.

Antioxidant and cytoprotective properties of high-density lipoproteins in vascular cells

Beside their key role in the regulation of cholesterol homeostasis, HDL exhibit antioxidant and anti-inflammatory properties that participate to their general antiatherogenic effect. The purpose of this review is to summarize the recent findings on antioxidant activity and cytoprotective cell signalling elicited by HDL against oxidized LDL and proatherogenic agents in vascular cells. HDL exhibit an antioxidant activity efficient to prevent LDL oxidation, or to inactivate newly formed lipid oxidation products. The antioxidant ability of HDL is due to the apoprotein moiety and to the presence of associated enzymes, paraoxonase and PAF-Acetyl Hydrolase. HDL prevent the intracellular oxidative stress and the inflammatory response elicited by oxidized LDL (ox-LDL), by inhibiting the NFkappaB signalling pathway, and the subsequent inflammatory events (expression of adhesion molecules, recruitment and proliferation of mononuclear cells within the vascular wall). HDL prevent ox-LDL-mediated cell activation and proliferation, this being also attributed to the presence in HDL of sphingosine-1 phosphate which modulates the migration and survival of vascular cells. Lastly, HDL inhibit apoptosis elicited by ox-LDL in vascular cells. Recent evidences indicate that, beside their strong antiatherogenic properties, HDL could exert their protective effect in diseases generally associated to inflammatory events.

D-4F decreases brain arteriole inflammation and improves cognitive performance in LDL receptor-null mice on a Western diet

LDL receptor-null mice on a Western diet (WD) have inflammation in large arteries and endothelial dysfunction in small arteries, which are improved with the apolipoprotein A-I mimetic D-4F. The role of hyperlipidemia in causing inflammation of very small vessels such as brain arterioles has not previously been studied. A WD caused a marked increase in the percent of brain arterioles with associated macrophages (microglia) (P < 0.01), which was reduced by oral D-4F but not by scrambled D-4F (ScD-4F; P < 0.01). D-4F (but not ScD-4F) reduced the percent of brain arterioles associated with CCL3/macrophage inflammatory protein-1alpha (P < 0.01) and CCL2/monocyte chemoattractant protein-1 (P < 0.001). A WD increased (P < 0.001) brain arteriole wall thickness and smooth muscle alpha-actin, which was reduced by D-4F but not by ScD-4F (P < 0.0001). There was no difference in plasma lipid levels, blood pressure, or arteriole lumen diameter with D-4F treatment. Cognitive performance in the T-maze continuous alternation task and in the Morris Water Maze was impaired by a WD and was significantly improved with D-4F but not ScD-4F (P < 0.05). We conclude that a WD induces brain arteriole inflammation and cognitive impairment that is ameliorated by oral D-4F without altering plasma lipids, blood pressure, or arteriole lumen size.

Hyperhomocysteinemia decreases circulating high-density lipoprotein by inhibiting apolipoprotein A-I Protein synthesis and enhancing HDL cholesterol clearance

We previously reported that hyperhomocysteinemia (HHcy), an independent risk factor of coronary artery disease (CAD), is associated with increased atherosclerosis and decreased plasma high-density lipoprotein cholesterol (HDL-C) in cystathionine beta-synthase-/apolipoprotein E-deficient (CBS(-/-)/apoE(-/-)) mice. We observed that plasma homocysteine (Hcy) concentrations are negatively correlated with HDL-C and apolipoprotein A1 (apoA-I) in patients with CAD. We found the loss of large HDL particles, increased HDL-free cholesterol, and decreased HDL protein in CBS(-/-)/apoE(-/-) mice, and attenuated cholesterol efflux from cholesterol-loaded macrophages to plasma in CBS(-/-)/apoE(-/-) mice. ApoA-I protein was reduced in the plasma and liver, but hepatic apoA-I mRNA was unchanged in CBS(-/-)/apoE(-/-) mice. Moreover, Hcy (0.5 to 2 mmol/L) reduced the levels of apoA-I protein but not mRNA and inhibited apoA-1 protein synthesis in mouse primary hepatocytes. Further, plasma lecithin:cholesterol acyltransferase (LCAT) substrate reactivity was decreased, LCAT specific activity increased, and plasma LCAT protein levels unchanged in apoE(-/-)/CBS(-/-) mice. Finally, the clearance of plasma HDL cholesteryl ester, but not HDL protein, was faster in CBS(-/-)/apoE(-/-) mice, correlated with increased scavenger receptor B1, and unchanged ATP-binding cassette transporter A1 protein expression in the liver. These findings indicate that HHcy inhibits reverse cholesterol transport by reducing circulating HDL via inhibiting apoA-I protein synthesis and enhancing HDL-C clearance.

Prognostic value of lipoproteins and their relation to inflammatory markers among patients with coronary artery disease

BACKGROUND

Lipoproteins and their subfractions are associated with the incidence of atherosclerotic diseases. In patients with coronary artery disease (CAD), low serum concentrations of high density lipoprotein (HDL) and high low-density lipoproteins (LDL) are correlated to myocardial infarction and cardiovascular death. There is growing evidence indicating that those lipoprotein factors are related to the inflammatory process in atherogenesis.

METHODS

We investigated in a median follow up of 3.9 years the association of HDL, apolipoprotein A-I (apoA-I), LDL, apolipoprotein B (apoB), and triglycerides with the incidence of a combined endpoint (myocardial infarction and cardiovascular death) and their relation to markers of inflammation in 1298 patients with angiographically documented CAD.

RESULTS

In univariate analysis, serum concentrations of apoA-I were significantly and inversely related to the combined endpoint, whereas serum concentrations of LDL, apoB, and triglycerides were not. HDL was not significantly related to the endpoint in univariate analyses (p=0.057). Multivariate analyses showed that only apoA-I is an independent predictor. ApoA-I (and HDL) was significantly related to markers of inflammation.

CONCLUSION

Serum apoA-I levels were an independent predictor for fatal and non-fatal cardiovascular events in patients with CAD. This may be related to its anti-inflammatory effect.

Antiinflammatory properties of HDL

There are several well-documented functions of high-density lipoprotein (HDL) that may explain the ability of these lipoproteins to protect against atherosclerosis. The best recognized of these is the ability of HDL to promote the efflux of cholesterol from cells. This process may minimize the accumulation of foam cells in the artery wall. However, HDL has additional properties that may also be antiatherogenic. For example, HDL is an effective antioxidant. The major proteins of HDL, apoA-I and apoA-II, as well as other proteins such as paraoxonase that cotransport with HDL in plasma, are well-known to have antioxidant properties. As a consequence, HDL has the capacity to inhibit the oxidative modification of low-density lipoprotein (LDL) in a process that reduces the atherogenicity of these lipoproteins. HDL also possesses other antiinflammatory properties. By virtue of their ability to inhibit the expression of adhesion molecules in endothelial cells, they reduce the recruitment of blood monocytes into the artery wall. These antioxidant and antiinflammatory properties of HDL may be as important as its cholesterol efflux function in terms of protecting against the development of atherosclerosis.

Reconstituted high-density lipoproteins inhibit the acute pro-oxidant and proinflammatory vascular changes induced by a periarterial collar in normocholesterolemic rabbits

BACKGROUND

HDLs have antiinflammatory and antioxidant properties in vitro. This study investigates these properties in vivo.

METHODS AND RESULTS

Chow-fed, normocholesterolemic New Zealand White rabbits received a daily infusion of (1) saline, (2) reconstituted HDL (rHDL) containing 25 mg apolipoprotein (apo) A-I and 50 mg of either 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC) or 1,2-dipalmitoyl phosphatidylcholine (DPPC), (3) 25 mg lipid-free apoA-I, or (4) 50 mg of either PLPC-small unilamellar vesicles (SUVs) or DPPC-SUVs on each of 3 consecutive days. Nonocclusive carotid periarterial collars were implanted after the second dose of treatment. Forty-eight hours after insertion of the collars, the arteries were removed and analyzed for the presence of reactive oxygen species, the infiltration of neutrophils, and the expression of adhesion proteins and chemokines. Insertion of the periarterial collar induced a 4.1-fold increase in presence of vascular wall reactive oxygen species. This effect was completely abolished in the animals infused with rHDL. The periarterial collar was associated with a dense infiltration of the arterial wall by polymorphonuclear leukocytes. This infiltration was inhibited by 73% to 94% in the animals infused with rHDL, by 75% in the animals infused with lipid-free apoA-I, and by 51% to 65% in animals infused with SUVs. There were no significant differences between the effects of PLPC and DPPC in either the rHDL or SUVs. Endothelial expression of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 was also increased by the collar insertion and inhibited by rHDL, lipid-free apoA-I, and, to a lesser extent, also by the SUVs.

CONCLUSIONS

Infusion of rHDL, apoA-I, and phospholipid-SUVs inhibits the early pro-oxidant and proinflammatory changes induced by a periarterial collar in normocholesterolemic rabbits.

Dyslipidemia associated with atherosclerotic disease systemically alters dendritic cell mobilization

High LDL and/or low HDL are risk factors for atherosclerosis and are also a common clinical feature in systemic lupus erythematosus, rheumatoid arthritis, and psoriasis. Here, we show that changes in lipid profiles that reflect atherosclerotic disease led to activation of skin murine dendritic cells (DCs) locally, promoted dermal inflammation, and induced lymph node hypertrophy. Paradoxically, DC migration to lymph nodes was impaired, suppressing immunologic priming. Impaired migration resulted from inhibitory signals generated by platelet-activating factor (PAF) or oxidized LDL that acts as a PAF mimetic. Normal DC migration and priming was restored by HDL or HDL-associated PAF acetylhydrolase (PAFAH), which mediates inactivation of PAF and oxidized LDL. Thus, atherosclerotic changes can sequester activated DCs in the periphery where they may aggravate local inflammation even as they poorly carry out functions that require their migration to lymph nodes. In this context, HDL and PAFAH maintain a normally functional DC compartment.

High-density lipoproteins retard the progression of atherosclerosis and favorably remodel lesions without suppressing indices of inflammation or oxidation

OBJECTIVE

Protective properties of high-density lipoproteins (HDL) may include reverse cholesterol transport and suppression of oxidation and inflammation. These were investigated in vivo, as were the effects of HDL on the characteristics of atherosclerotic lesions.

METHODS AND RESULTS

Male apolipoprotein E knockout (apoE-/-) and apoE-/- mice expressing human apolipoprotein AI (hAI/apoE-/-) were studied up to 20 weeks after commencing a high-fat diet. Plasma HDL cholesterol was twice as high in hAI/apoE-/- mice. Over time, aortic root lesion area remained less in hAI/apoE-/- mice, although plaques became complex. In advanced lesions, plaque lipid was higher in apoE-/- mice, whereas plaque collagen and alpha actin were increased in hAI/apoE-/- mice. In nonlesional aorta, mRNA abundance for pro-inflammatory proteins (vascular cell adhesion molecule [VCAM]-1, intercellular adhesion molecule-1 [ICAM-1], monocyte chemoattractant protein-1 [MCP-1]) increased between 4 and 16 weeks in apoE-/- (but not wild-type) mice, and were not reduced by elevated HDL. Autoantibodies to malondialdehyde low-density lipoprotein (LDL) increased progressively in apoE-/- mice, with similar results in hAI/apoE-/- mice.

CONCLUSIONS

HDL retarded plaque size progression despite greatly elevated plasma cholesterol. This effect was over a wide range of lesion severity. Expression of hAI reduced plaque lipid and increased the proportion of plaque occupied by collagen and smooth muscle cells, but did not affect indicators of inflammation or LDL oxidation.

Low high-density lipoprotein cholesterol: physiological background, clinical importance and drug treatment

Low high-density lipoprotein (HDL) cholesterol is an important risk factor for coronary heart disease (CHD). In vitro, HDL exerts several potentially anti-atherogenic activities. HDLs mediate the reverse cholesterol transport (RCT) from peripheral cells to the liver, inhibit oxidation of low-density lipoprotein (LDL), adhesion of monocytes to the endothelium, apoptosis of vascular endothelial and smooth muscle cells and platelet activation, and stimulate the endothelial secretion of vasoactive substances as well as smooth muscle cell proliferation. Hence, raising HDL-cholesterol levels has become an interesting target for anti-atherosclerotic drug therapy. Levels of HDL cholesterol and the composition of HDL subclasses in plasma are regulated by apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors and cellular transporters. The interplay of these factors leads to RCT and determines the composition and, thereby, the anti-atherogenic properties of HDL. Several inborn errors of metabolism, as well as genetic animal models, are characterised by both elevated HDL cholesterol and increased rather than decreased cardiovascular risk. These findings suggest that the mechanism of HDL modification rather than simply increasing HDL cholesterol determine the efficacy of anti-atherosclerotic drug therapy. In several controlled and prospective intervention studies, patients with low HDL cholesterol and additional risk factors benefited from treatment with fibric acid derivatives (fibrates) or HMG-CoA reductase inhibitors (statins). However, only in some trials was prevention of coronary events in patients with low HDL cholesterol and hypertriglyceridaemia related to an increase in HDL cholesterol. We discuss the clinical and metabolic effects of fibrates, statins, nicotinic acid and sex steroids, and present novel therapeutic strategies that show promise in modifying HDL metabolism. In conclusion, HDL-cholesterol levels increase only moderately after treatment with currently available drugs and do not necessarily correlate with the functionality of HDL. Therefore, the anti-atherosclerotic therapy of high-risk cardiovascular patients should currently be focused on the correction of other risk factors present besides low HDL cholesterol. However, modification of HDL metabolism and improvement of RCT remain an attractive target for the development of new regimens of anti-atherogenic drug therapy.

Design, Synthesis, and Biological Evaluation of Thio-Containing Compounds with Serum HDL-Cholesterol-Elevating Properties

A novel series of substituted sulfanyldihydroimidazolones (1) that modulates high-density lipoprotein cholesterol (HDL-C) has been reported to have HDL-elevating properties in several animal models. Concerns about the chemical and metabolic stability of 1 directed us to explore the structure-activity relationship (SAR) of a related series of substituted thiohydantoins (2). Expansion of the scope of the thiohydantoin series led to exploration of compounds in related thio-containing ring systems 3-7 and the N-cyanoguanidine derivative 8. Compounds were tested sequentially in three animal models to assess their HDL-C elevating efficacy and safety profiles. Further evaluation of selected compounds in a dose-response paradigm culminated in the identification of compound 2.39 as a candidate compound for advanced preclinical studies.

Lack of inhibitory effect of HDL on TNFalpha-induced adhesion molecule expression in human aortic endothelial cells

Monocyte adhesion to and transmigration across the endothelium are initiating steps in atherogenesis. Cytokine-induced adhesion molecule expression in human umbilical vein endothelial cells (HUVEC) has been reported to be inhibited by either native HDL or reconstituted discoidal HDL (rHDL). In the present study we investigated these putative anti-atherosclerotic effects of HDL and rHDL in a more physiologically relevant cell type, i.e. human aortic endothelial cells (HAEC). HDL isolated by ultracentrifugation from eleven healthy subjects or rHDL made with apoA-I and either 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (PLPC), or 1,2-dimyristoyl-sn-glycero-3-phosphocholine was incubated for 16 h with HAEC prior to stimulation with tumor necrosis factor-alpha (TNFalpha, 100 U/ml). Expression of E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was measured by cell ELISA and Northern blot analysis. HDL (0.25, 0.5, 1.0 and 2.0 mgprotein/ml) failed to significantly inhibit TNFalpha-induced mRNA and protein expression of all three adhesion molecules. Furthermore, of the three rHDL preparations (16 micromol/l apoA-I) only that containing the polyunsaturated PLPC significantly reduced TNFalpha-induced VCAM-1 expression (by 29.9+/-9.1%). These data contrast with previously reported results using plasma HDL and HUVEC, and show that human HDL and rHDL, except for PLPC-rHDL, are ineffective inhibitors of TNFalpha-induced adhesion molecule expression in HAEC. The ability of polyunsaturated phospholipids in HDL to affect endothelial activation remains to be further investigated.

High-density lipoproteins and atherosclerosis

High-density lipoproteins (HDLs) are strongly related to risk of atherosclerotic cardiovascular disease. Low levels of HDL cholesterol are a major cardiovascular risk factor, and overexpression of the major HDL protein, apolipoprotein (apo) A-I, markedly inhibits progression and even induces regression of atherosclerosis in animal models. Clinical data regarding the effect of increasing HDL cholesterol on vascular events are limited. HDL remains an important potential target for therapeutic intervention. A variety of gene products are involved in the regulation of HDL metabolism. Yet, the mechanisms by which HDL inhibits atherosclerosis are not yet fully understood. There remains much to be learned about HDL metabolism and its relation to atherosclerosis and other cardiovascular risk factors.

Four strains of spontaneously hyperlipidemic (SHL) mice: phenotypic distinctions determined by genetic backgrounds

Spontaneously hyperlipidemic (SHL) mice are Japanese wild mice (KOR) with disruption of the apolipoprotein E (Apo E) gene. These mice (KOR-Apoe(shl)) are superhypercholesterolemic and develop severe xanthoma, but their atherosclerosis is relatively mild compared with Apo E knockout mice. First, we tested whether this distinction is due to additional mutation of the Apoc1 and/or Apoc2 genes in KOR-Apoe(shl). Southern blot analysis, but found no gross disruption of these genes. Next, we tested whether the phenotypic distinction is due to differences in the genetic background. To this end, we established three lines of congenic SHL mice with a genetic background of C57BL/6, BALB/c or C3H/He, and named them, respectively, C57BL/6.KOR-Apoe(shl) (B6.KOR-Apoe(shl)), BALB/c.KOR-Apoe(shl) (C.KOR-Apoe(shl)) and C3H/He.KOR-Apoe(shl) (C3.KOR-Apoe(shl)). Hypercholesterolemia was most severe in KOR-Apoe(shl) followed the by others as follows; KOR-Apoe(shl)>>C3.KOR-Apoe(shl)>C.KOR-Apoe(shl)>B6.KOR-Apoe(shl). In contrast, atherosclerosis was most severe in B6.KOR Apoe(shl) followed by the others: B6.KOR-Apoe(shl)>C.KOR-Apoe(shl)>>C3.KOR-Apoe(shl)> or =KOR-Apoe(shl). This order, however, did not match that in xanthoma, which was highly prominent in KOR-Apoe(shl) but mild in B6.KOR-Apoe(shl), C.KOR-Apoe(shl) and C3.KORApoe(shl). This order, however, did not match that in xanthoma, which was highly prominant in KOR-Apoe(shl) but mild in B6.KOR-Apoe(shl), C.KOR-Apoe(shl) and C3.KOR-Apoe(shl). These distinctions suggest that the severity of each of the phenotypes is determined by distinct genetic backgrounds which probably are composed of polymorphism of lipid metabolism-related proteins. We found that apolipoprotein A-I is decreased in each SHL strain and polymorphic between B6.KOR-Apoe(shl) and the other strains examined. This polymorphism may be related to the most severe atherosclerosis observed in B6.KOR-Apoe(shl). It is most likely that combination of such polymorphisms is due to the genetic background accountable for phenotype distinctions.

MRI and characterization of atherosclerotic plaque: emerging applications and molecular imaging

Noninvasive high-resolution magnetic resonance has the potential to image atherosclerotic plaque and to determine its composition and microanatomy. This review summarizes the rationale for plaque imaging and describes the characteristics of plaque by use of existing MRI techniques. The use of MRI in human disease and in animal models, particularly in rabbits and mice, is presented. Present and future applications of MRI, including real-time vascular intervention, new contrast agents, and molecular imaging, are also discussed.

Effect of high-density lipoproteins on the expression of adhesion molecules in endothelial cells

There are several potential mechanisms by which HDLs protect against atherosclerosis. One relates to the ability of HDLs to promote the efflux of cholesterol from macrophages. Another is the ability of HDLs to inhibit one of the earliest events in the development of atherosclerosis, namely the expression of vascular cell adhesion molecules in activated endothelial cells. This property has been reported in vitro in studies with both native and reconstituted HDLs. The inhibitory activity of reconstituted HDLs is influenced by the phospholipid composition of the particles. An inhibition of endothelial cell adhesion molecule expression has also been observed in some (but not all) studies conducted in vivo in mice and pigs. The mechanism of this potentially anti-atherogenic effect of HDLs remains uncertain, as does its contribution to the cardioprotective effects of HDLs in vivo.

HDL and arteriosclerosis: beyond reverse cholesterol transport

The inverse correlation between serum levels of high density lipoprotein (HDL) cholesterol and the risk of coronary heart disease, the protection of susceptible animals from atherosclerosis by transgenic manipulation of HDL metabolism, and several potentially anti-atherogenic in vitro-properties have made HDL metabolism an interesting target for pharmacological intervention in atheroslcerosis. We have previously reviewed the concept of reverse cholesterol transport, which describes both the metabolism and the classic anti-atherogenic function of HDL (Arterioscler. Thromb. Vasc. Biol. 20 2001 13). We here summarize the current understanding of additional biological, potentially anti-atherogenic properties of HDL. HDL inhibits the chemotaxis of monocytes, the adhesion of leukocytes to the endothelium, endothelial dysfunction and apoptosis, LDL oxidation, complement activation, platelet activation and factor X activation but also stimulates the proliferation of endothelial cells and smooth muscle cells, the synthesis of prostacyclin and natriuretic peptide C in endothelial cells, and the activation of proteins C and S. These anti-inflammatory, anti-oxidative, anti-aggregatory, anti-coagulant, and pro-fibrinolytic activities are exerted by different components of HDL, namley apolipoproteins, enzymes, and even specific phospholipids. This complexity further emphasizes that changes in the functionality of HDL rather than changes of plasma HDL-cholesterol levels determine the anti-atherogenicity of therapeutic alterations of HDL metabolism.

Serum paraoxonase activity and the extent of lipid peroxidation are not affected by increased levels of human apolipoprotein A-I: studies in transgenic mice

The present study analyzed the effect of increased concentrations of human apolipoprotein (apo) A-I in transgenic mice serum on paraoxonase activity and on lipid peroxidation. In the transgenic mice serum, in comparison to control (non-transgenic) C57BL/6 mice, we found high concentrations of human apoA-I and high-density lipoprotein (HDL)-cholesterol, but serum lipid peroxidation (basal and free radical-induced) and serum paraoxonase activity were similar in the two mouse groups. Comparing the individual results, no significant correlation was found between free radical-induced serum lipid peroxidation and apoA-I concentrations. Serum paraoxonase activity also did not correlate with serum concentrations of human apoA-I. However, a significant inverse relationship (R2=0.75) was observed between the individual values of paraoxonase activity and free radical-induced lipid peroxidation in both mouse groups. Direct analysis of the effect of pure human apoA-I and paraoxonase (using the specific paraoxonase inhibitor PD-92770) on lipid peroxidation also revealed that paraoxonase, but not apoA-I, protects serum lipids from oxidation. We thus conclude that the increased human apoA-I concentration in the mouse serum neither affect serum paraoxonase activity, nor protects against lipid peroxidation, whereas paraoxonase significantly inhibits serum lipid peroxidation.

Elevating high-density lipoprotein cholesterol in apolipoprotein E-deficient mice remodels advanced atherosclerotic lesions by decreasing macrophage and increasing smooth muscle cell content

BACKGROUND

HDL cholesterol levels are inversely correlated with coronary heart disease risk in humans, and in animal studies, HDL elevation decreases formation and progression of foam-cell lesions. The potential for HDL to affect preexisting advanced atherosclerotic lesions is not known. To approach this issue, we used a novel mouse aortic transplantation model.

METHODS AND RESULTS

ApoE-deficient (EKO) mice were fed a Western-type diet for 6 months, and thoracic aortic segments containing advanced lesions replaced segments of the abdominal aorta of 4-month-old EKO syngeneic mice not expressing (plasma HDL cholesterol approximately 26 mg/dL) or expressing (HDL approximately 64 mg/dL) a human apoAI (hAI) transgene. Both types of recipients had comparable non-HDL cholesterol levels. Five months after transplantation, mice were killed and grafts analyzed. Compared with lesion area in pretransplant mice (0.14+/-0.04 mm(2), mean+/-SEM), there was progression in the EKO recipients (0.39+/-0.06 mm(2), P<0.01). Compared with EKO recipients, hAI/EKO recipients had retarded progression (0.24+/-0.04 mm(2), P<0.05). Immunostaining for CD68 and other macrophage-associated proteins, monocyte chemoattractant protein-1, acyl coenzyme A:cholesterol acyltransferase, and tissue factor, in lesions of pretransplant and EKO recipient mice showed abundant macrophages. In contrast, compared with any other group, lesional macrophage area in hAI/EKO mice decreased >80% (P<0.003), and smooth muscle cell content (alpha-actin staining) increased >300% (P<0.006). The decrease in macrophages and increase in smooth muscle cells was primarily in the superficial subendothelial layer.

CONCLUSIONS

Increasing HDL cholesterol levels in EKO mice retards progression of advanced atherosclerotic lesions and remodels them to a more stable-appearing phenotype.

Adhesion of monocytes to arterial endothelium and initiation of atherosclerosis are critically dependent on vascular cell adhesion molecule-1 gene dosage

- Vascular cell adhesion molecule-1 (VCAM-1/Vcam1) is a cytokine-inducible member of the immunoglobulin gene superfamily that is expressed by arterial endothelial cells in regions predisposed to atherosclerosis and at borders of atherosclerotic plaques. To determine whether VCAM-1 expression regulates atherosclerotic lesion formation, we crossed Vcam1 domain 4-deficient (D4D) mice, which partially circumvent the embryonic lethality of Vcam1 null mice, with apolipoprotein E null (Apoe(-/-)) mice, which spontaneously develop hypercholesterolemia and atherosclerosis. In the Apoe(-/-) background, mice homozygous for the Vcam1 D4D allele had markedly reduced arterial VCAM-1 expression, monocyte adherence in the aortic root, and fatty streak formation. Heterozygous Vcam1 D4D mice revealed a Vcam1 gene-dosage effect and had intermediate, yet significant, reductions in these parameters. Our data demonstrate that VCAM-1 plays a pivotal role in the initiation of atherosclerosis in Apoe(-/-) mice.

Time sequence of the inhibition of endothelial adhesion molecule expression by reconstituted high density lipoproteins

We have used discoidal reconstituted high density lipoproteins (rHDL) containing apolipoprotein (apo) A-I and dimyristoyl phosphatidylcholine (DMPC) as a tool to investigate the time sequence of the HDL-mediated inhibition of vascular cell adhesion molecule (VCAM)-1 and E-selectin expression in cytokine-activated human umbilical vein endothelial cells (HUVECs). Specifically, we have asked a few questions - (i) how long do the cells need to be exposed to the rHDL before adhesion molecule expression is inhibited and (ii) how long does the inhibition persist after removing the rHDL from the cells. When the cells were not pre-incubated with the rHDL, there was no inhibition. The magnitude of the inhibition increased progressively with increasing duration of pre-incubation up to 16 h. Inhibition did not require the rHDL to be physically present during the activation of adhesion molecule expression by tumour necrosis factor(TNF)-alpha, excluding the possibility that the rHDL was merely interfering with the interaction between TNF-alpha and the cells. When HUVECs were pre-incubated for 16 h with rHDL, the inhibition remained substantial even if the rHDL were removed from the medium up to 8 h prior to addition of TNF-alpha. The HDL-mediated inhibition of VCAM-1 in HUVECs was unaffected by the presence of puromycin, an inhibitor of protein synthesis, excluding the possibility that HDL may have acted by stimulating the synthesis of a cell protein that itself inhibits adhesion molecule expression. These results have important implications in terms of understanding the mechanism(s) of the HDL-mediated inhibition of endothelial adhesion molecule expression.

Mouse models of atherosclerosis

Atherosclerosis bears many features of a chronic inflammation that affects the intima of large and medium-sized arteries. In recent years apolipoprotein E-deficient and LDL receptor-deficient mice have been used to examine the effects of various gene products on the development of atherosclerosis. In the present review the effects of genetics, apolipoprotein E, inflammatory gene modifiers, lipoprotein modifications, lipoprotein receptors, vessel wall expression of lipoprotein-metabolizing enzymes, and the atheroprotective role of HDL on atherosclerosis in these mice are discussed. The importance of examining lesions that are more advanced than fatty streaks and careful histologic and immunologic examination of lesion composition is emphasized.