Recombinant LCAT (Lecithin:Cholesterol Acyltransferase) Rescues Defective HDL (High-Density Lipoprotein)-Mediated Endothelial Protection in Acute Coronary Syndrome.

Objective- Aim of this study was to evaluate changes in LCAT (lecithin:cholesterol acyltransferase) concentration and activity in patients with an acute coronary syndrome, to investigate if these changes are related to the compromised capacity of HDL (high-density lipoprotein) to promote endothelial nitric oxide (NO) production, and to assess if rhLCAT (recombinant human LCAT) can rescue the defective vasoprotective HDL function. Approach and Results- Thirty ST-segment-elevation myocardial infarction (STEMI) patients were enrolled, and plasma was collected at hospital admission, 48 and 72 hours thereafter, at hospital discharge, and at 30-day follow-up. Plasma LCAT concentration and activity were measured and related to the capacity of HDL to promote NO production in cultured endothelial cells. In vitro studies were performed in which STEMI patients' plasma was added with rhLCAT and HDL vasoprotective activity assessed by measuring NO production in endothelial cells. The plasma concentration of the LCAT enzyme significantly decreases during STEMI with a parallel significant reduction in LCAT activity. HDL isolated from STEMI patients progressively lose the capacity to promote NO production by endothelial cells, and the reduction is related to decreased LCAT concentration. In vitro incubation of STEMI patients' plasma with rhLCAT restores HDL ability to promote endothelial NO production, possibly related to significant modification in HDL phospholipid classes. Conclusions- Impairment of cholesterol esterification may be a major factor in the HDL dysfunction observed during acute coronary syndrome. rhLCAT is able to restore HDL-mediated NO production in vitro, suggesting LCAT as potential therapeutic target for restoring HDL functionality in acute coronary syndrome.

Complete and Partial Lecithin:Cholesterol Acyltransferase Deficiency Is Differentially Associated With Atherosclerosis.

BACKGROUND: Lecithin:cholesterol acyltransferase (LCAT) is the sole enzyme that esterifies cholesterol in plasma. Its role in the supposed protection from atherogenesis remains unclear because mutations in LCAT causing fish-eye disease (FED) or familial LCAT deficiency (FLD) have been reported to be associated with more or instead less carotid atherosclerosis, respectively. This discrepancy may be associated with the loss of cholesterol esterification on only apolipoprotein AI (FED) or on both apolipoprotein AI- and apolipoprotein B-containing lipoproteins (FLD), an aspect that has thus far not been investigated. METHODS: Seventy-four heterozygotes for LCAT mutations recruited from Italy and the Netherlands were assigned to FLD (n=33) or FED (n=41) groups and compared with 280 control subjects. Subclinical atherosclerosis was assessed with carotid intima-media thickness. RESULTS: Compared with control subjects, total cholesterol was lower by 16% (-32.9 mg/dL) and 7% (-14.9 mg/dL) and high-density lipoprotein cholesterol was lower by 29% (-16.7 mg/dL) and 36% (-20.7 mg/dL) in the FLD and FED groups, respectively. Subjects with FLD displayed a significant 18% lower low-density lipoprotein cholesterol compared with subjects with FED (101.9±35.0 versus 123.6±47.4 mg/dL; P=0.047) and control subjects (122.6±35.0 mg/dL; P=0.003). Remarkably, all 3 intima-media thickness parameters were lower in subjects with FLD compared with FED and control subjects (accounting for age, sex, body mass index, smoking, hypertension, family history of cardiovascular disease, and plasma lipids). After additional correction for nationality and ultrasonographic methods, average and maximum intima-media thickness remained significantly lower when subjects with FLD were compared with those with FED (0.59 versus 0.73 mm, P=0.003; and 0.87 versus 1.24 mm, P<0.001, respectively). In contrast, the common carotid intima-media thickness (corrected for age, sex, body mass index, smoking, hypertension, family history of cardiovascular disease, and plasma lipids) was higher in subjects with FED compared with control subjects (0.69 versus 0.65 mm; P=0.05), but this significance was lost after adjustment for nationality and ultrasonographic machine. CONCLUSIONS: In this head-to-head comparison, FLD and FED mutations were shown to be associated with decreased and increased atherosclerosis, respectively. We propose that this discrepancy is related to the capacity of LCAT to generate cholesterol esters on apolipoprotein B-containing lipoproteins. Although this capacity is lost in FLD, it is unaffected in FED. These results are important when considering LCAT as a target to decrease atherosclerosis.

Plasma PCSK9 levels and lipoprotein distribution are preserved in carriers of genetic HDL disorders.

Proprotein convertase subtilisin/kexin 9 (PCSK9), a protein regulating the number of cell-surface LDL receptors (LDLR), circulates partially associated to plasma lipoproteins. How this interaction alters PCSK9 plasma levels is still unclear. In the present study, we took advantage of the availability of a large cohort of carriers of genetic HDL disorders to evaluate how HDL defects affect plasma PCSK9 levels and its distribution among lipoproteins. Plasma PCSK9 concentrations were determined by ELISA in carriers of mutations in LCAT, ABCA1, or APOAI genes, and lipoprotein distribution was analyzed by FPLC. Carriers of one or two mutations in the LCAT gene show plasma PCSK9 levels comparable to that of unaffected family controls (homozygotes, 159.4 ng/mL (124.9;243.3); heterozygotes, 180.3 ng/mL (127.6;251.5) and controls, 190.4 ng/mL (146.7;264.4); P for trend = 0.33). Measurement of PCSK9 in plasma of subjects carrying mutations in ABCA1 or APOAI genes confirmed normal values. When fractionated by FPLC, PCSK9 peaked in a region between LDL and HDL in control subjects. In carriers of all HDL defects, lipoprotein profile shows a strong reduction of HDL, but the distribution of PCSK9 was superimposable to that of controls. In conclusion, the present study demonstrates that in genetically determined low HDL states plasma PCSK9 concentrations and lipoprotein distribution are preserved, thus suggesting that HDL may not be involved in PCSK9 transport in plasma.

Depletion in LpA-I:A-II particles enhances HDL-mediated endothelial protection in familial LCAT deficiency.

The aim of this study was to evaluate the vasoprotective effects of HDL isolated from carriers of LCAT deficiency, which are characterized by a selective depletion of LpA-I:A-II particles and predominance of preß migrating HDL. HDLs were isolated from LCAT-deficient carriers and tested in vitro for their capacity to promote NO production and to inhibit vascular cell adhesion molecule-1 (VCAM-1) expression in cultured endothelial cells. HDLs from carriers were more effective than control HDLs in promoting eNOS activation with a gene-dose-dependent effect (PTrend = 0.048). As a consequence, NO production induced by HDL from carriers was significantly higher than that promoted by control HDL (1.63 ± 0.24-fold vs. 1.34 ± 0.07-fold, P = 0.031). HDLs from carriers were also more effective than control HDLs in inhibiting the expression of VCAM-1 (homozygotes, 65.0 ± 8.6%; heterozygotes, 53.1 ± 7.2%; controls, 44.4 ± 4.1%; PTrend = 0.0003). The increased efficiency of carrier HDL was likely due to the depletion in LpA-I:A-II particles. The in vitro findings might explain why carriers of LCAT deficiency showed flow-mediated vasodilation and plasma-soluble cell adhesion molecule concentrations comparable to controls, despite low HDL-cholesterol levels. These results indicate that selective depletion of apoA-II-containing HDL, as observed in carriers of LCAT deficiency, leads to an increased capacity of HDL to stimulate endothelial NO production, suggesting that changes in HDL apolipoprotein composition may be the target of therapeutic interventions designed to improve HDL functionality.

HDL and atherosclerosis: Insights from inherited HDL disorders.

Plasma high density lipoproteins (HDL) comprise a highly heterogeneous family of lipoprotein particles, differing in density, size, surface charge, and lipid and protein composition. Epidemiological studies have shown that plasma HDL level inversely correlates with atherosclerotic cardiovascular disease. The most relevant atheroprotective function of HDL is to promote the removal of cholesterol from macrophages within the arterial wall and deliver it to the liver for excretion in a process called reverse cholesterol transport. In addition, HDLs can contribute to the maintenance of endothelial cell homeostasis and have potent antioxidant properties. It has been long suggested that individual HDL subclasses may differ in terms of their functional properties, but which one is the good particle remains to be defined. Inherited HDL disorders are rare monogenic diseases due to mutations in genes encoding proteins involved in HDL metabolism. These disorders are not only characterized by extremely low or high plasma HDL levels but also by an abnormal HDL subclass distribution, and thus represent a unique tool to understand the relationship between plasma HDL concentration, HDL function, and HDL-mediated atheroprotection. This article is part of a Special Issue entitled Linking transcription to physiology in lipodomics.

Effects of established hypolipidemic drugs on HDL concentration, subclass distribution, and function.

The knowledge of an inverse relationship between plasma high-density lipoprotein cholesterol (HDL-C) concentrations and rates of cardiovascular disease has led to the concept that increasing plasma HDL-C levels would be protective against cardiovascular events. Therapeutic interventions presently available to correct the plasma lipid profile have not been designed to specifically act on HDL, but have modest to moderate effects on plasma HDL-C concentrations. Statins, the first-line lipid-lowering drug therapy in primary and secondary cardiovascular prevention, have quite modest effects on plasma HDL-C concentrations (2-10%). Fibrates, primarily used to reduce plasma triglyceride levels, also moderately increase HDL-C levels (5-15%). Niacin is the most potent available drug in increasing HDL-C levels (up to 30%), but its use is limited by side effects, especially flushing.The present chapter reviews the effects of established hypolipidemic drugs (statins, fibrates, and niacin) on plasma HDL-C levels and HDL subclass distribution, and on HDL functions, including cholesterol efflux capacity, endothelial protection, and antioxidant properties.

Recombinant human LCAT normalizes plasma lipoprotein profile in LCAT deficiency.

Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for cholesterol esterification in plasma. Mutations in the LCAT gene leads to two rare disorders, familial LCAT deficiency and fish-eye disease, both characterized by severe hypoalphalipoproteinemia associated with several lipoprotein abnormalities. No specific treatment is presently available for genetic LCAT deficiency. In the present study, recombinant human LCAT was expressed and tested for its ability to correct the lipoprotein profile in LCAT deficient plasma. The results show that rhLCAT efficiently reduces the amount of unesterified cholesterol (-30%) and promotes the production of plasma cholesteryl esters (+210%) in LCAT deficient plasma. rhLCAT induces a marked increase in HDL-C levels (+89%) and induces the maturation of small preß-HDL into alpha-migrating particles. Moreover, the abnormal phospholipid-rich particles migrating in the LDL region were converted in normally sized LDL.

Plasma lecithin:cholesterol acyltransferase and carotid intima-media thickness in European individuals at high cardiovascular risk.

Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for cholesterol esterification in plasma. LCAT is a major factor in HDL remodeling and metabolism, and it has long been believed to play a critical role in macrophage reverse cholesterol transport (RCT). The effect of LCAT on human atherogenesis is still controversial. In the present study, the plasma LCAT concentration was measured in all subjects (n = 540) not on drug treatment at the time of enrollment in the multicenter, longitudinal, observational IMPROVE study. Mean and maximum intima-media thickness (IMT) of the whole carotid tree was measured by B-mode ultrasonography in all subjects. In the entire cohort, LCAT quartiles were not associated with carotid mean and maximum IMT (P for trend 0.95 and 0.18, respectively), also after adjustment for age, gender, HDL-cholesterol (HDL-C), and triglycerides. No association between carotid IMT and LCAT quartiles was observed in men (P=0.30 and P=0.99 for mean and maximum IMT, respectively), whereas carotid IMT increased with LCAT quartiles in women (P for trend 0.14 and 0.019 for mean and maximum IMT, respectively). The present findings support the concept that LCAT is not required for an efficient reverse cholesterol transport and that a low plasma LCAT concentration and activity is not associated with increased atherosclerosis.

[LCAT deficiency: a nephrological diagnosis]. / Il deficit di LCAT: una diagnosi nefrologica.

A genetic mendelian autosomal recessive condition of deficiency of lecithin- cholesterol acyltransferase (LCAT) can produce two different diseases: one highly interesting nephrologic picture of complete enzymatic deficiency (lecithin:cholesterol acyltransferase deficiency; OMIM ID #245900; FLD), characterized by the association of dyslipidemia, corneal opacities, anemia and progressive nephropathy; and a partial form (fish eye disease; OMIM ID #136120; FED) with dyslipidemia and progressive corneal opacities only. The diagnosis of FLD falls first of all under the competence of nephrologists, because end-stage renal disease appears to be its most severe outcome. The diagnostic suspicion is based on clinical signs (corneal opacities, more severe anemia than expected for the degree of chronic renal failure, progressive proteinuric nephropathy) combined with histology obtained by kidney biopsy (glomerulopathy evolving toward sclerosis with distinctive lipid deposition). However, the final diagnosis, starting with a finding of extremely low levels of HDL-cholesterol, requires collaboration with lipidology Centers that can perform sophisticated investigations unavailable in common laboratories. To be heterozygous for a mutation of the LCAT gene is one of the monogenic conditions underlying primary hypoalphalipoproteinemia (OMIM ID #604091). This disease, which is characterized by levels of HDL-cholesterol below the 5th percentile of those of the examined population (<28 mg/dL for Italians), has heritability estimates between 40% and 60% and is considered to be a predisposing condition for coronary artery disease. Nevertheless, some monogenic forms, and especially those associated with LCAT deficiency, seem to break the rule, confirming once more the value of a proper diagnosis before drawing prognostic conclusions from a laboratory marker. As in many other rare illnesses, trying to discover all the existing cases will contribute to allow studies broad enough to pave the way for further therapies, in this case also fostering the production by industries of the lacking enzyme by genetic engineering. Epidemiological studies, although done on selected populations such as hypoalphalipoproteinemia patients on dialysis and with the effective genetic tools of today, have been disappointing in elucidating the disease. Spreading the clinical knowledge of the disease and its diagnostic course among nephrologists seems to be the best choice, and this is the aim of our work.

Functional lecithin: cholesterol acyltransferase is not required for efficient atheroprotection in humans.

BACKGROUND: Mutations in the LCAT gene cause lecithin:cholesterol acyltransferase (LCAT) deficiency, a very rare metabolic disorder with 2 hypoalphalipoproteinemia syndromes: classic familial LCAT deficiency (Online Mendelian Inheritance in Man No. 245900), characterized by complete lack of enzyme activity, and fish-eye disease (Online Mendelian Inheritance in Man No. 136120), with a partially defective enzyme. Theoretically, hypoalphalipoproteinemia cases with LCAT deficiency should be at increased cardiovascular risk because of high-density lipoprotein deficiency and defective reverse cholesterol transport. METHODS AND RESULTS: The extent of preclinical atherosclerosis was assessed in 40 carriers of LCAT gene mutations from 13 Italian families and 80 healthy controls by measuring carotid intima-media thickness (IMT). The average and maximum IMT values in the carriers were 0.07 and 0.21 mm smaller than in controls (P=0.0003 and P=0.0027), respectively. Moreover, the inheritance of a mutated LCAT genotype had a remarkable gene-dose-dependent effect in reducing carotid IMT (P=0.0003 for average IMT; P=0.001 for maximum IMT). Finally, no significant difference in carotid IMT was found between carriers of LCAT gene mutations that cause total or partial LCAT deficiency (ie, familial LCAT deficiency or fish-eye disease). CONCLUSIONS: Genetically determined low LCAT activity in Italian families is not associated with enhanced preclinical atherosclerosis despite low high-density lipoprotein cholesterol levels. This finding challenges the notion that LCAT is required for effective atheroprotection and suggests that elevating LCAT expression or activity is not a promising therapeutic strategy to reduce cardiovascular risk.

Structure and function of the apoA-IV T347S and Q360H common variants.

Human apolipoprotein A-IV (apoA-IV) is involved in chylomicron assembly and secretion, and in reverse cholesterol transport. Several apoA-IV isoforms exist, the most common in Caucasian populations being apoA-IV-1a (T347S) and apoA-IV-2 (Q360H). The objective of the present study was to investigate the impact of these common aminoacid substitutions on the ability of apoA-IV to bind lipids, to promote cell cholesterol efflux via ABCA1, and to maintain endothelial homeostasis. Recombinant forms of wild-type apoA-IV, apoA-IV Q360H, and apoA-IV T347S were produced in Escherichia coli. ApoA-IV Q360H and apoA-IV T347S showed a slightly higher alpha-helical content compared to wild-type apoA-IV, and associated with phospholipids faster than wild-type apoA-IV. The capacity to promote ABCA1-mediated cholesterol efflux was significantly greater for the apoA-IV T347S than the other apoA-IV isoforms. No differences were observed in the ability of apoA-IV isoforms to inhibit the production of VCAM-1 and IL-6 in TNFalpha-stimulated endothelial cells. In conclusion, the apoA-IV T347S common variant has increased lipid binding properties and cholesterol efflux capacity, while the apoA-IV Q360H variant has only slightly increased lipid binding properties. The two common aminoacid substitutions have no effect on the ability of apoA-IV to maintain endothelial homeostasis.

Small discoidal pre-beta1 HDL particles are efficient acceptors of cell cholesterol via ABCA1 and ABCG1.

The aim of this study was to correlate the lipid content and size of discoidal reconstituted HDL particles with their ability to promote cellular cholesterol efflux. Homogeneous discoidal rHDL particles containing apoA-I and POPC, with diameters of 7.8, 9.6, 10.8, 12.5, and 17.0 nm, were prepared by the cholate dialysis technique. Cholesterol efflux to rHDL was evaluated in pathway-specific cell models for ABCA1-, ABCG1-, and SR-BI-mediated efflux. ABCA1-mediated efflux was efficiently promoted by the 7.8 nm rHDL containing 82 POPC molecules per particle. This rHDL also promoted ABCG1, but not SR-BI, cholesterol efflux. All large and lipid-rich rHDLs, with a diameter of >or=9.6 nm and a phospholipid content of >/=202 molecules per particle, promoted both SR-BI- and ABCG1-mediated efflux. Our results indicated that the ABCA1-mediated cell cholesterol efflux can be efficiently driven not only by monomolecular lipid free/poor apoA-I but also by a small discoidal phospholipid-containing particle resembling plasma pre-beta1 HDL. This same particle also promotes ABCG1- but not SR-BI-mediated efflux. These results help to clarify the role of plasma pre-beta1 HDL in reverse cholesterol transport.

Normal vascular function despite low levels of high-density lipoprotein cholesterol in carriers of the apolipoprotein A-I(Milano) mutant.

BACKGROUND: Carriers of the apolipoprotein A-I(Milano) (apoA-I(M)) mutant have very low plasma high-density lipoprotein cholesterol (HDL-C) levels but do not show any history of premature cardiovascular disease or any evidence of preclinical vascular disease. HDL is believed to prevent the development of vascular dysfunction, which may well contribute to HDL-mediated atheroprotection. Whether the low HDL level of apoA-I(M) carriers is associated with impaired vascular function is presently unknown. METHODS AND RESULTS: The vascular response to reactive hyperemia, assessed by measuring postischemic increase in forearm arterial compliance, and the plasma concentration of soluble cell adhesion molecules were evaluated in 21 adult apoA-I(M) carriers, 21 age- and gender-matched nonaffected relatives (control subjects), and 21 healthy subjects with low HDL-C (low-HDL subjects). The average plasma HDL-C and apoA-I levels of apoA-I(M) carriers were remarkably lower than those of control subjects and significantly lower than those of low-HDL subjects. The postischemic increase in forearm arterial compliance in the apoA-I(M) carriers was 2-fold greater than in low-HDL subjects and remarkably similar to that of control subjects. Plasma soluble cell adhesion molecule levels were similar in apoA-I(M) carriers and control subjects but were greater in low-HDL subjects. When incubated with endothelial cells, HDL isolated from apoA-I(M) carriers was more effective than HDL from control and low-HDL subjects in stimulating endothelial nitric oxide synthase expression and activation and in downregulating tumor necrosis factor-alpha-induced expression of vascular cell adhesion molecule-1. CONCLUSIONS: Despite their very low HDL levels, apoA-I(M) carriers do not display typical features of impaired vascular function because of an improved activity of apoA-I(M) HDL in maintaining endothelial cell homeostasis.

Anti-inflammatory and cardioprotective activities of synthetic high-density lipoprotein containing apolipoprotein A-I mimetic peptides.

Apolipoprotein A-I (apoA-I) mimetic peptides may represent an alternative to apoA-I for large-scale production of synthetic high-density lipoproteins (sHDL) as a therapeutic agent. In this study, the cardioprotective activity of sHDL made with either L37pA peptide or its d-stereoisomer, D37pA, was compared to sHDL made with apoA-I. The peptides were reconstituted with palmitoyl-oleoyl-phosphatidylcholine, which yielded sHDL particles comparable to apoA-I sHDL in diameter, molecular weight, and alpha-helical content. Pretreatment of endothelial cells with either peptide sHDL reduced tumor necrosis factor alpha-stimulated vascular cell adhesion molecule-1 expression to the same extent as apoA-I sHDL. In an isolated rat heart model of ischemia/reperfusion (I/R) injury, L37pA and D37pA sHDL significantly reduced postischemic cardiac contractile dysfunction compared to the saline control, as indicated by a 49.7 +/- 6.4% (L37pA; P < 0.001) and 53.0 +/- 9.1% (D37pA; P < 0.001) increase of left ventricular-developed pressure (LVDP) after reperfusion and by a 45.4 +/- 3.4% (L37pA; P < 0.001) and 49.6 +/- 2.6% (D37pA; P < 0.001) decrease of creatine kinase (CK) release. These effects were similar to the 51.3 +/- 3.0% (P < 0.001) increase of LVDP and 51.3 +/- 3.0 (P < 0.001) reduction of CK release induced by apoA-I sHDL. Consistent with their cardioprotective effects, all three types of sHDL particles mediated an approximate 20% (P < 0.001) reduction of cardiac tumor necrosis factor alpha (TNFalpha) content and stimulated an approximate 35% (P < 0.05) increase in postischemic release of prostacyclin. In summary, L37pA and D37pA peptides can form sHDL particles that retain a similar level of protective activity as apoA-I sHDL on the endothelium and the heart; thus, apoA-I mimetic peptides may be useful therapeutic agents for the prevention of cardiac I/R injury.

Synthetic HDL as a new treatment for atherosclerosis regression: has the time come?

Plasma high-density lipoprotein cholesterol (HDL-C) has received considerable attention as a potential therapeutic target to further reduce cardiovascular events in the statin era. One therapeutic approach to enhance HDL-mediated atheroprotection involves the use of small, synthetic and orally-active compounds that substantially raise plasma HDL-C levels. However, doubts on the clinical benefit achievable with such treatments have been raised by the premature termination of a large Phase III trial with torcetrapib, the most potent and furthest developed HDL-C raising compound, because of excess mortality in patients receiving the drug. The alternative is the direct administration of synthetic HDL (sHDL), discoidal lipoprotein particles which mimic most, if not all, of the atheroprotective properties of plasma HDL. Short-term treatments with sHDL of different composition caused consistent and remarkable reductions of atheroma volume in patients with acute coronary syndromes (ACS). Although at early stages of drug development, sHDL hold vast promise for plaque stabilization/regression, and cardiovascular event reduction.

High Density Lipoproteins Inhibit Oxidative Stress-Induced Prostate Cancer Cell Proliferation.

Recent evidence suggests that oxidative stress can play a role in the pathogenesis and the progression of prostate cancer (PCa). Reactive oxygen species (ROS) generation is higher in PCa cells compared to normal prostate epithelial cells and this increase is proportional to the aggressiveness of the phenotype. Since high density lipoproteins (HDL) are known to exert antioxidant activities, their ability to reduce ROS levels and the consequent impact on cell proliferation was tested in normal and PCa cell lines. HDL significantly reduced basal and H2O2-induced oxidative stress in normal, androgen receptor (AR)-positive and AR-null PCa cell lines. AR, scavenger receptor BI and ATP binding cassette G1 transporter were not involved. In addition, HDL completely blunted H2O2-induced increase of cell proliferation, through their capacity to prevent the H2O2-induced shift of cell cycle distribution from G0/G1 towards G2/M phase. Synthetic HDL, made of the two main components of plasma-derived HDL (apoA-I and phosphatidylcholine) and which are under clinical development as anti-atherosclerotic agents, retained the ability of HDL to inhibit ROS production in PCa cells. Collectively, HDL antioxidant activity limits cell proliferation induced by ROS in AR-positive and AR-null PCa cell lines, thus supporting a possible role of HDL against PCa progression.

Synthetic high density lipoproteins for the treatment of myocardial ischemia/reperfusion injury.

Synthetic high density lipoproteins (sHDL) are discoidal lipoprotein particles made of an apolipoprotein and a phospholipid, which mimic most, if not all, of the atheroprotective properties of plasma HDL, including stimulation of reverse cholesterol transport (RCT), prevention of endothelial dysfunction, and inhibition of lipid oxidation. sHDL are currently under development as a novel treatment for atherosclerotic cardiovascular disease. A number of preclinical studies have demonstrated the ability of single or multiple injections of sHDL to induce the regression of atherosclerotic plaques and prevent arterial restenosis. In the first phase II trial in patients with acute coronary syndromes, a short-term treatment with sHDL containing the disulfide-linked dimer of the apolipoprotein A-IMilano variant (A-IM/A-IM) caused a remarkable reduction of atheroma volume. sHDL also display a direct cardioprotective activity in ex vivo and in vivo models of myocardial ischemia/reperfusion (I/R) injury, and may become a useful adjunctive therapy to improve clinical outcomes in patients with acute coronary syndromes or undergoing coronary procedures.

High-density lipoproteins attenuate interleukin-6 production in endothelial cells exposed to pro-inflammatory stimuli.

The purpose of the present study was to investigate the ability of high-density lipoproteins (HDL) to attenuate endothelial dysfunction, by assessing down-regulation of cytokine-induced interleukin-6 (IL-6) production in cultured endothelial cells, and measuring plasma IL-6 levels in three groups of healthy individuals with low, average, or high plasma HDL-cholesterol. Human plasma HDL caused a concentration-dependent inhibition of TNFalpha-induced IL-6 production in human endothelial cells (by 58.5+/-1.5% at 2 mg of HDL-protein/ml). Reconstituted HDL made with apolipoprotein A-I (apoA-I) and phosphatidylcholine were as effective as plasma HDL, while lipid-free apoA-I or phosphatidylcholine liposomes had no effect. HDL attenuated IL-6 mRNA levels, an effect which occurs through inhibition of p38 MAP kinase. The median plasma IL-6 concentration was significantly higher in subjects with low HDL-cholesterol (2.54 pg/ml) compared with those with average or high HDL-cholesterol (1.31 pg/ml and 1.47 pg/ml, respectively). When all subjects were considered together, a lower HDL-cholesterol was the strongest independent predictor of higher IL-6 (F=25.38, P<0.001). By inhibiting IL-6 production and lowering plasma IL-6 concentration, HDL may limit the pro-atherogenic effects of both acute and chronic inflammatory states, of which IL-6 is a key orchestrator.

Inhibition of MMP-2 activation and release as a novel mechanism for HDL-induced cardioprotection.

High density lipoproteins (HDL) protect the heart against ischemia/reperfusion (I/R) injury, and matrix metalloproteinase-2 (MMP-2) directly contributes to cardiac contractile dysfunction after I/R. To investigate the possible involvement of MMP-2 inhibition in HDL-mediated cardioprotection, isolated rat hearts underwent 20 min of low-flow ischemia and 30 min of reperfusion. Plasma-derived and synthetic HDL attenuated the I/R-induced cardiac MMP-2 activation and release in a dose-dependent way. The attenuation of I/R-induced MMP-2 activation by HDL correlated with the reduction of post-ischemic contractile dysfunction and cardiomyocyte necrosis. These results indicate prevention of MMP-2 activation as a novel mechanism for HDL-mediated cardioprotection.

Structure, function and amyloidogenic propensity of apolipoprotein A-I.

Apolipoprotein A-I, the major structural apolipoprotein of high-density lipoproteins, efficiently protects humans from cholesterol accumulation in tissues; however, it can cause systemic amyloidosis in the presence of peculiar amino acid replacements. The wild-type molecule also has an intrinsic tendency to generate amyloid fibrils that localise within the atherosclerotic plaques. The structure, folding and metabolism of normal apolipoprotein A-I are extremely complex and as yet not completely clarified, but their understanding appears essential for the elucidation of the amyloid transition. We reviewed present knowledge on the structure, function and amyloidogenic propensity of apolipoprotein A-I with the aim of highlighting the possible molecular mechanisms that might contribute to the pathogenesis of this disease. Important clues on apolipoprotein A-I amyloidogenesis may be obtained from classical comparative studies of the properties of the wild-type versus the amyloidogenic counterpart. Additionally, in the case of apoA-I, further insights on the molecular mechanisms underlying its amyloidogenic propensity may derive from comparative studies between amyloidogenic variants and other mutations associated with hypoalphalipoproteinemia without amyloidosis.