Low-density Lipoprotein Clearance Research Articles

Management of hypercholesterolemia for prevention of atherosclerotic cardiovascular disease: focus on the potential role of recombinant anti-PCSK9 monoclonal antibodies.

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death and disability in the United States and other developed nations, and is rising rapidly in the rest of the world. Low-density lipoprotein (LDL) is the major atherogenic particle in most patients at high risk for ASCVD events, and statin-based LDL-lowering treatment is the major focus of treatment for prevention of ASCVD. Despite this, an estimated 57 million US adults (25%) still have moderately elevated levels of LDL-cholesterol (LDL-C) > 160 mg/dL, and many others have an LDL-C above the level considered appropriate for their high-risk status. Although statins are very effective for lowering LDL-C, and other classes of LDL-lowering medications are available, many patients still cannot achieve adequate LDL-lowering with maximal tolerated doses of US Food and Drug Administration-approved treatments. Thus, there is an unmet medical need for statin adjuncts in these patients, as well as for statin alternatives in statin-intolerant patients. A recently discovered human protein, proprotein convertase subtilisin/kexin type 9 (PCSK9), plays an important role in LDL metabolism by promoting degradation of the LDL receptor, and thus reducing clearance of LDL and increasing LDL-C levels. Accordingly, inhibition of PCSK9 activity has become an attractive target for drug development for lowering LDL-C, and human monoclonal antibodies against PCSK9, are now in late-stage clinical development. These antibodies are at least as effective as statins for LDL-C lowering (or more so), and their effects are additive to those of statins. To date, they have been well tolerated and apparently safe in clinical trials. Long-term randomized, controlled trials of their safety, tolerability, and ability to reduce ASCVD are now underway.

Clearance of Plasma Proprotein Convertase Subtilisin/Kexin 9 by Low-Density Lipoprotein Apheresis

Proprotein convertase subtilisin/kexin 9 (PCSK9) is a secreted protein that modulates plasma low-density lipoprotein (LDL) concentrations in part by facilitating degradation of the LDL receptor. It also mediates degradation of the very-low density lipoprotein receptor and apolipoprotein E receptor 2. PCSK9 in plasma is primarily secreted by hepatocytes and is thought to have paracrine and exocrine effects, but the role of circulating PCSK9 in the modulation of LDL clearance from plasma remains unclear.1 Insights into the partitioning of PCSK9 in plasma were provided by recent studies published by Tavori, Fazio, and colleagues that demonstrated a high degree of binding of PCSK9 to LDL particles in plasma,2 as well as the data published in Circulation Research showing a 52±5% clearance of PCSK9 from plasma during LDL apheresis.3 The removal of PCSK9 during LDL apheresis seemed to be mediated predominantly by sequestration of 81% of LDL-bound …

Combinational effects of farnesoid X receptor antagonist and statin on plasma lipid levels and low-density lipoprotein clearance in guinea pigs

AimsWe previously reported anti-dyslipidemic effects of a farnesoid X receptor antagonist in monkeys. In this study, we compared the cholesterol-lowering effects of single and combined administration of a farnesoid X receptor antagonist, compound-T8, and the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor atorvastatin in a guinea pig model. Main methodsPlasma levels of 7α-hydroxy-4-cholesten-3-one, a marker of hepatic cholesterol 7α-hydroxylase activity, were measured after a single administration of compound-T8. The effects of compound-T8 or atorvastatin on plasma cholesterol levels and low-density lipoprotein (LDL) clearance were investigated after 14 or 16days of repeated dosing, respectively. Fractional catabolic rate of plasma LDL was estimated by intravenous injection of DiI-labeled human LDL. The cholesterol-lowering effects of combination therapy were investigated after 7days of repeated treatment. Key findingsCompound-T8 (10 and 30mg/kg) increased plasma 7α-hydroxy-4-cholesten-3-one levels in a dose-dependent manner. Single administration of compound-T8 (30mg/kg) and atorvastatin (30mg/kg) reduced plasma non-high-density lipoprotein (non-HDL) cholesterol levels by 48% and 46%, respectively, and increased clearance of plasma DiI-labeled LDL by 29% and 35%, respectively. Compound-T8 (10mg/kg) or atorvastatin (10mg/kg) reduced non-HDL cholesterol levels by 19% and 25%, respectively, and combination therapy showed an additive effect and lowered cholesterol levels by 48%. SignificanceSimilar to atorvastatin, compound-T8 reduced plasma non-HDL cholesterol levels accompanied with accelerated LDL clearance in guinea pigs. Combination therapy additively decreased plasma non-HDL cholesterol levels. Therefore, monotherapy with a farnesoid X receptor antagonist and combination therapy of a farnesoid X receptor antagonist with atorvastatin would be attractive dyslipidemia treatment options.

Select Articles Published on the Topic of Coronary Heart Disease in 2013

Select Articles Published on the Topic of Coronary Heart Disease in 2013

Use of microsomal triglyceride transfer protein inhibitors in patients with homozygous familial hypercholesterolemia: translating clinical trial experience into clinical practice.

Homozygous familial hypercholesterolemia (HoFH) is associated with severe hypercholesterolemia and premature cardiovascular morbidity and mortality. The most frequent cause of HoFH is loss of function mutations in the gene for the low-density lipoprotein receptor, resulting in reduced clearance of low-density lipoprotein (LDL) cholesterol from the circulation. Patients with HoFH have attenuated responsiveness to lipidlowering therapies such as statins, cholesterol absorption inhibition, and bile acid binding resins because of impaired LDL receptor expression. Lomitapide is a novel microsomal triglyceride transfer protein inhibitor that does not depend on the ability to upregulate LDL receptors on the surface of hepatocytes. Lomitapide reduces production of apolipoprotein B-containing lipoproteins, significantly reduces serum levels of LDL cholesterol, and is approved for use in patients with HoFH in the United States and the European Union.

Statin therapy is a major determinant of PCSK9 plasma concentration: data from four clinical trials with AMG 145

Purpose: Proprotein convertase subtilisin kexin type 9 (PCSK9) plays a critical role in the metabolism of low density lipoproteins (LDL), impairing LDL clearance by promoting LDL receptor degradation. Data suggest statins may modify PCSK9 levels. We tested whether PCSK9 levels were associated with the intensity of statin therapy. Method: We analyzed baseline PCSK9 plasma concentrations in 1335 patients, aged 18-80, in four Phase 2 clinical trials (MENDEL, LAPLACE, RUTHERFORD, GAUSS) with AMG 145, a fully human monoclonal antibody to PCSK9, and examined associations with baseline characteristics, including statin therapy (none, non-intensive, or intensive [defined as simvastatin 80 mg QD, atorvastatin ≥40 mg QD, rosuvastatin ≥20 mg QD, or any statin plus ezetimibe]). Results: Baseline PCSK9 concentration varied greatly (median 406 ng/mL, IQR 326-493 ng/mL, range 116-1200 ng/mL), but levels were not associated with age, sex, or LDL-C. PCSK9 levels did significantly differ based on statin therapy; medians were 343 ng/mL (IQR 296-408) in patients on no statin, 421 ng/mL (IQR 346-485) for those on non-intensive statin treatments, and 531 ng/mL (IQR 433-645) for those on intensive statin treatments (p-value < 0.0001). In the analyses of log transformed baseline PCKSK9 levels, baseline statin treatment accounted for more than one-quarter (R2=0.28, p-value < 0.0001) of the variability, more than any other baseline factor. ![Figure][1] Baseline PCKS9 by Baseline Statin Use Conclusions: PCSK9 plasma concentrations are higher in patients on statin therapy and highest in those on the most intensive statin or statin plus ezetimibe treatments. [1]: pending:yes

Circulation: Clinical Summaries

<i>Circulation:</i> Clinical Summaries

A DNA Microarray for the Detection of Point Mutations and Copy Number Variation Causing Familial Hypercholesterolemia in Europe

To facilitate genetic cascade screening for familial hypercholesterolemia (FH) in Europe, two versions (7 and 9) of a DNA microarray were developed to detect the most frequent point mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin 9 (PCSK9) genes. The design of these microarrays is based on LIPOchip, version 4, which detects 191 LDLR and APOB mutations identified in Spanish patients with FH. A major improvement of LIPOchip, versions 7 and 9, is the ability to detect copy number variation (deletions or duplications of entire exons) in LDLR, thus abolishing the need to perform multiplex ligase-dependent probe amplification in patients with FH. The aim of this study was to validate a tool capable of detecting point mutations and copy number variations simultaneously and to evaluate its use and the newly developed software for analysis in clinical practice by reanalysis of several patients with known mutations causing FH. With the help of these validations, several aspects were analyzed, improved, and implemented in a newer version, which was evaluated through an internal validation.

A combined LDL receptor/LDL receptor adaptor protein 1 mutation as the cause for severe familial hypercholesterolemia

Familial hypercholesterolemia (FH) results from impaired catabolism of plasma low density lipoproteins (LDL), thus leading to high cholesterol, atherosclerosis, and a high risk of premature myocardial infarction. FH is commonly caused by defects of the LDL receptor or its main ligand apoB, together mediating cellular uptake and clearance of plasma LDL. In some cases FH is inherited by mutations in the genes of PCSK9 and LDLRAP1 (ARH) in a dominant or recessive trait. The encoded proteins are required for LDL receptor stability and internalization within the LDLR pathway. To detect the underlying genetic defect in a family of Turkish descent showing unregular inheritance of severe FH, we screened the four candidate genes by denaturing gradient gel electrophoresis (DGGE) mutation analysis. We identified different combinatory mixtures of LDLR- and LDLRAP1-gene defects as the cause for severe familial hypercholesterolemia in this family. We also show for the first time that a heterozygous LDLR mutation combined with a homozygous LDLRAP1 mutation produces a more severe hypercholesterolemia phenotype in the same family than a homozygous LDLR mutation alone.

Exon Skipping of Hepatic APOB Pre-mRNA With Splice-switching Oligonucleotides Reduces LDL Cholesterol In Vivo

Familial hypercholesterolemia (FH) is a genetic disorder characterized by extremely high levels of plasma low-density lipoprotein (LDL), due to defective LDL receptor-apolipoprotein B (APOB) binding. Current therapies such as statins or LDL apheresis for homozygous FH are insufficiently efficacious at lowering LDL cholesterol or are expensive. Treatments that target APOB100, the structural protein of LDL particles, are potential therapies for FH. We have developed a series of APOB-directed splice-switching oligonucleotides (SSOs) that cause the expression of APOB87, a truncated isoform of APOB100. APOB87, like similarly truncated isoforms expressed in patients with a different condition, familial hypobetalipoproteinemia, lowers LDL cholesterol by inhibiting very low-density lipoprotein (VLDL) assembly and increasing LDL clearance. We demonstrate that these "APO-skip " SSOs induce high levels of exon skipping and expression of the APOB87 isoform, but do not substantially inhibit APOB48 expression in cell lines. A single injection of an optimized APO-skip SSO into mice transgenic for human APOB resulted in abundant exon skipping that persists for >6 days. Weekly treatments generated a sustained reduction in LDL cholesterol levels of 34-51% in these mice, superior to pravastatin in a head-to-head comparison. These results validate APO-skip SSOs as a candidate therapy for FH.

When It Looks Like Familial Hypercholesterolemia…but Is Not

When faced with a new patient whose low-density lipoprotein (LDL) cholesterol level is 239 mg/dL, who has no other diseases, and who takes no drugs affecting lipid metabolism, a doctor is likely to make the diagnosis of Familial Hypercholesterolemia (FH) on the spot. If the patient confirms that she has had this problem since she was a young girl and that her father and older brother are affected as well, this will close the case. However, even if she objects that her cholesterol was normal when she was in college and swears that her parents have no lipid problems, our confidence in the diagnosis will not falter, and we would just assume that personal and family history may not be accurately recalled. We all know that the criteria for the diagnosis of FH are more complex, but xanthomas and arcus senilis are rarely present, and thickening of the Achilles tendons is hard to confirm by manual examination, coronary artery disease is often delayed in subjects without other risk factors, and evaluation of family history in most cases is based on patient report, not on direct investigation. This leaves us with 1 piece of information, the LDL cholesterol level, which we know can be moderately increased by many factors and raises above the 95th percentile (or about 190 mg/dL in adults) only for severe clearance problems. In the absence of renal, hepatic, autoimmune, or thyroid diseases, if the patients are not taking medications that notoriously can raise LDL cholesterol levels, an LDL clearance problem is attributable to a faulty interaction between the LDL receptor (LDLR) and its ligand on the LDL particle (apoB). Classically, FH was defined as a dominantly inherited disease caused by mutations in the LDLR gene.1 It was later determined that a dysfunctional mutation in apoB also …

Altered Metabolism of Low-Density Lipoprotein and Very-Low-Density Lipoprotein Remnant in Autosomal Recessive Hypercholesterolemia

Background— Autosomal recessive hypercholesterolemia (ARH) exhibits different responsiveness to statins compared with that in homozygous familial hypercholesterolemia (FH). However, few data exist regarding lipoprotein metabolism of ARH. Therefore, we aimed to clarify lipoprotein metabolism, especially the remnant lipoprotein fractions of ARH before and after statin therapy. Methods and Results— We performed a lipoprotein kinetic study in an ARH patient and 7 normal control subjects, using stable isotope methodology (10 mg/kg of [ 2 H 3 ]-leucine). These studies were performed at baseline and after the 20 mg daily dose of atorvastatin. Tracer/tracee ratio of apolipoprotein B (apoB) was determined by gas chromatography/mass spectrometry and fractional catabolic rates (FCR) were determined by multicompartmental modeling, including remnant lipoprotein fractions. FCR of low-density lipoprotein (LDL) apoB of ARH was significantly lower than those of control subjects (0.109 versus 0.450±0.122 1/day). In contrast, the direct removal of very-low-density lipoprotein remnant was significantly greater in ARH than those in control subjects (47.5 versus 2±2%). Interestingly, FCR of LDL apoB in ARH dramatically increased to 0.464 1/day, accompanying reduction of LDL cholesterol levels from 8.63 to 4.22 mmol/L after treatment with atorvastatin of 20 mg/d for 3 months. Conclusions— These results demonstrate that ARH exhibits decreased LDL clearance associated with decreased FCR of LDL apoB and increased clearance for very-low-density lipoprotein remnant. We suggest that increased clearance of remnant lipoprotein fractions could contribute to the great responsiveness to statins, providing new insights into the lipoprotein metabolism of ARH and the novel pharmacological target for LDLRAP1.

LRP6 Protein Regulates Low Density Lipoprotein (LDL) Receptor-mediated LDL Uptake

Genetic variations in LRP6 gene are associated with high serum LDL cholesterol levels. We have previously shown that LDL clearance in peripheral B-lymphocytes of the LRP6(R611C) mutation carriers is significantly impaired. In this study we have examined the role of wild type LRP6 (LRP6(WT)) and LRP6(R611C) in LDL receptor (LDLR)-mediated LDL uptake. LDL binding and uptake were increased when LRP6(WT) was overexpressed and modestly reduced when it was knocked down in LDLR-deficient CHO (ldlA7) cells. These findings implicated LRP6 in LDLR-independent cellular LDL binding and uptake. However, LRP6 knockdown in wild type CHO cells resulted in a much greater decline in LDL binding and uptake compared with CHO-ldlA7 cells, suggesting impaired function of the LDLR. LDLR internalization was severely diminished when LRP6 was knocked down and was restored after LRP6 was reintroduced. Further analysis revealed that LRP6(WT) forms a complex with LDLR, clathrin, and ARH and undergoes a clathrin-mediated internalization after stimulation with LDL. LDLR and LRP6 internalizations as well as LDL uptake were all impaired in CHO-k1 cells expressing LRP6(R611C). These studies identify LRP6 as a critical modulator of receptor-mediated LDL endocytosis and introduce a mechanism by which variation in LRP6 may contribute to high serum LDL levels.

Shedding of Syndecan–1 From Human Hepatocytes Alters Very Low Density Lipoprotein Clearance

We recently showed that the heparan sulfate proteoglycan syndecan-1 mediates hepatic clearance of triglyceride-rich lipoproteins in mice based on systemic deletion of syndecan-1 and hepatocyte-specific inactivation of sulfotransferases involved in heparan sulfate biosynthesis. Here, we show that syndecan-1 expressed on primary human hepatocytes and Hep3B human hepatoma cells can mediate binding and uptake of very low density lipoprotein (VLDL). Syndecan-1 also undergoes spontaneous shedding from primary human and murine hepatocytes and Hep3B cells. In human cells, phorbol myristic acid induces syndecan-1 shedding, resulting in accumulation of syndecan-1 ectodomains in the medium. Shedding occurs through a protein kinase C-dependent activation of ADAM17 (a disintegrin and metalloproteinase 17). Phorbol myristic acid stimulation significantly decreases DiD (1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate)-VLDL binding to cells, and shed syndecan-1 ectodomains bind to VLDL. Although mouse hepatocytes appear resistant to induced shedding in vitro, injection of lipopolysaccharide into mice results in loss of hepatic syndecan-1, accumulation of ectodomains in the plasma, impaired VLDL catabolism, and hypertriglyceridemia. These findings suggest that syndecan-1 mediates hepatic VLDL turnover in humans as well as in mice and that shedding might contribute to hypertriglyceridemia in patients with sepsis.

HMG-CoA reductase inhibitor augments the serum total cholesterol-lowering effect of human adipose tissue-derived multilineage progenitor cells in hyperlipidemic homozygous Watanabe rabbits

Familial hypercholesterolemia (FH) is an autosomal codominant disease characterized by high concentrations of proatherogenic lipoproteins secondary to deficiency in low-density lipoprotein (LDL) receptor. We reported recently the use of in situ stem cell therapy of human adipose tissue-derived multilineage progenitor cells (hADMPCs) in lowering serum total cholesterol in the homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits, an animal model of homozygous FH. Here we demonstrate that pravastatin, an HMG-CoA reductase inhibitor, augmented the cholesterol-lowering effect of transplanted hADMPCs and enhanced LDL clearance in homozygous WHHL rabbit. The results suggest the potential beneficial effects of in situ stem cell therapy in concert with appropriately selected pharmaceutical agents, in regenerative medicine.

Interleukin-17 and Atherosclerotic Vascular Disease

Atherosclerotic vascular disease (ASVD) involves several overlapping pathological processes. Atherogenesis, the process by which atherosclerotic plaques develop in the arterial wall, involves inspissation of abnormal circulating lipoproteins into the vessel intima, resulting in inflammation, injury, and responses to injury.1 Mouse models of atherogenesis, involving impaired low-density lipoprotein clearance due to gene knockout of either apolipoprotein E (ApoE) or low-density lipoprotein receptor, are widely used to study this process. The presence of plaques in humans sets the stage for complications, such as plaque rupture or fissure that stimulate thrombosis; intraplaque hemorrhages that may rapidly cause luminal impingement; more gradual but progressive vascular stenoses due to inadequate outward remodeling that produce chronic ischemia; inflammatory aneurysms with the potential for catastrophic events, such as aortic rupture; or plaque embolization, leading to infarcts in tissues distal to the plaque site. Each of these complications arises from distinct but overlapping causes, of which inflammation is a significant component.2 Mouse models for the study of these complications have significant limitations. See accompanying article on page 1565 Inflammation in ASVD is best described as chronic active, involving acute exacerbations superimposed on a more persistent, indolent process. The initial trigger for inflammation in the vessel wall may be innate immunity, an inflammatory process that is activated by myeloid cells or some types of innate lymphocytes recognizing conserved motifs in microbe-derived molecules or of endogenous molecules that are released as a consequence of cell injury. Recognition …

Diffuse Involvement of Aorta in Patient with Familial Hyperlipidemia

Familial hyperlipidemia (FH) is an inherited metabolic disorder caused by low-density lipoprotein (LDL) receptor abnormality. The delayed clearance of serum LDL results in severe hypercholesterolemia, which leads to the accumulation of LDL-derived cholesterol in skin, tendons, and arterial walls.In homozygous form of the disease, severely atheromatous involvement of the aorta extending to the coronary ostia is almost always present, and particular surgical strategy is required to prevent atheroembolic events.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

540 Adverse Reactions in Statin Therapy at Younger and Children Older Then Twelve Years

Background: Obesity in childhood bodes ill for future cardiovascular risk. HMG-CoA reductase is an enzyme in the cholesterol biosynthetic pathway that catalyses the conversion of HMG-CoA to mevalonic acid. Statins are a class of drugs that lower the level of cholesterol in the blood by reducing the production of cholesterol by the liver. Aims: The most controversial change appears to have been the inclusion of statins as potential firstline pharmacologic agents in older children. Methods: High-risk children, include those who are obese or overweight and who also have high blood pressure, or diabetes, or a positive family history of either high cholesterol or early heart disease. The safety of statins in children and adolescents is based on trials that have ranged in duration from six months to one year. Results: Inhibition of this enzyme in the liver results in decreased cholesterol synthesis as well as increased synthesis of LDL receptors, resulting in an increased clearance of low-density lipoprotein (LDL) from the bloodstream. The first results can be seen after one week of use and the effect is maximal after four to six weeks. No serious laboratory adverse events were reported during follow-up, and statin treatment had no untoward effects on sexual maturation. Conclusion: The recommendation to use statins in childhood seems to have hit a collective nerve, perhaps awakening us to the fuller implications of the obesity epidemic. Statins exhibit action beyond lipid-lowering activity in the prevention of atherosclerosis.

Transplantation of Human Adipose Tissue-Derived Multilineage Progenitor Cells Reduces Serum Cholesterol in Hyperlipidemic Watanabe Rabbits

Familial hypercholesterolemia (FH) is an autosomal codominant disease characterized by high concentrations of proatherogenic lipoproteins and premature atherosclerosis secondary to low-density lipoprotein (LDL) receptor deficiency. We examined a novel cell therapy strategy for the treatment of FH in the Watanabe heritable hyperlipidemic (WHHL) rabbit, an animal model for homozygous FH. We delivered human adipose tissue-derived multilineage progenitor cells (hADMPCs) via portal vein and followed by immunosuppressive regimen to avoid xenogenic rejection. Transplantation of hADMPCs resulted in significant reductions in total cholesterol, and the reductions were observed within 4 weeks and maintained for 12 weeks. (125)I-LDL turnover study showed that the rate of LDL clearance was significantly higher in the WHHL rabbits with transplanted hADMPCs than those without transplanted. After transplantation hADMPCs were localized in the portal triad, subsequently integrated into the hepatic parenchyma. The integrated cells expressed human albumin, human alpha-1-antitrypsin, human Factor IX, human LDL receptors, and human bile salt export pump, indicating that the transplanted hADMPCs resided, survived, and showed hepatocytic differentiation in vivo and lowered serum cholesterol in the WHHL rabbits. These results suggested that hADMPC transplantation could correct the metabolic defects and be a novel therapy for inherited liver diseases.