Low Density Lipoprotein Receptor Activity Research Articles

MicroRNA-mediated Regulation of LDL Receptor: Biological and Pharmacological Implications.

One of the main causes of atherosclerosis is a disruption in cellular cholesterol hemostasis. The low-density lipoprotein receptor (LDLR) is an important factor in maintaining cholesterol homeostasis by the receptor-mediated endocytosis of LDL particles. Defective hepatic LDLR activity and uptake of LDL particles lead to elevated blood levels of low-density lipoprotein cholesterol (LDL-C), which is associated with a higher risk of atherosclerotic cardiovascular disease. LDLR expression can be affected by microRNAs (miRNAs). Some miRNAs, like miR-148a, miR-185, miR-224, miR-520, miR-128-1, miR-27a/b, miR-130b, and miR-301 seem to be important post-transcriptional regulators of LDLR related genes. These findings indicate the critical role of miRNAs in regulating LDL metabolism. The aim of this review was to provide insight into the miRNAs involved in LDLR activity and their potential roles in the treatment of cardiovascular disease.

Evolocumab Treatment in Pediatric Patients With Homozygous Familial Hypercholesterolemia: Pooled Data From Three Open-Label Studies.

Pediatric patients with homozygous familial hypercholesterolemia (HoFH) have an increased risk of atherosclerotic cardiovascular disease and difficulty meeting low-density lipoprotein cholesterol (LDL-C) goals. In this post hoc analysis, we evaluated pooled safety and efficacy data from 3 studies in pediatric patients with HoFH treated with the PCSK9 (proprotein convertase subtilisin/kexin type 9) monoclonal antibody inhibitor evolocumab. Patients with HoFH aged 10 to 17 years received treatment with open-label evolocumab 420 mg subcutaneously monthly or biweekly in the TAUSSIG, RAMAN, or HAUSER-OLE clinical studies. All patients received background statins with or without ezetimibe. Study duration ranged from 12 to 260 weeks. The primary end point was treatment-emergent adverse events per 100 patient-years. Efficacy end points were changes from baseline to week 12 in lipids and PCSK9. Of the 39 patients in the pooled analysis, 69.2% were males, median age was 13.0 years, and 79.5% (31/39) had genotyped HoFH with LDLR pathogenic variants. Overall, median exposure to evolocumab was 18.2 (Q1, Q3: 3.0, 18.5) months. Treatment-emergent adverse events with an exposure-adjusted patient incidence rate of ≥5% were upper respiratory tract infection (6.6%), influenza (5.2%), and acne (5.0%) per 100 patient-years. Exposure-adjusted patient incidence of serious treatment-emergent adverse events was 13.3% per 100 patient-years. Excluding 4 patients receiving lipoprotein apheresis, week 12 median percentage change from baseline in LDL-C was -2.9% (Q1, Q3: -21.7, 1.5); however, 42.9% (15/35) of patients achieved ≥15% reduction in LDL-C from baseline. Residual LDLR (LDL receptor) activity was not associated with a reduction in LDL-C. In this pooled data analysis from 3 studies in pediatric patients with HoFH, evolocumab was well tolerated, with no new safety signals reported. These safety findings are consistent with findings from previous studies of evolocumab. Patients showed marked variability in LDL-C reduction. Results from this pooled analysis support guidelines suggesting a trial of PCSK9 inhibitor therapy regardless of estimated residual LDLR function. URL: https://www.clinicaltrials.gov; Unique identifier: NCT01624142, NCT03403374, and NCT02624869.

Low-density Lipoprotein Receptor Activities, Lipids, Apolipoprotein, and Clinical Course of Patients with Steroid-resistant Nephrotic Syndrome Treated with Low-density Lipoprotein Apheresis: A Case Series.

We herein report three cases of steroid-resistant nephrotic syndrome successfully treated with low-density lipoprotein apheresis (LDL-A). All patients were treated with a combination of steroids, cyclosporine, and LDL-A. In all cases, the serum concentrations of LDL, total and high-density lipoprotein cholesterol, and triglycerides were significantly lowered following LDL-A administration. Furthermore, the estimated LDL receptor activity increased, while both serum LDL and total cholesterol levels decreased, suggesting that LDL-A increases LDL receptor activity by driving changes in serum cholesterol concentration. This case series suggests that LDL-A increases LDL receptor activity, which may improve the intracellular uptake of cyclosporine.

Novel LDLR variants affecting low density lipoprotein metabolism identified in familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is an autosomal dominant disease of lipid metabolism mainly caused by mutations in the low-density lipoprotein receptor (LDLR) gene. Genetic detection of patients with FH help with precise diagnosis and treatment, thus reducing the risk of coronary heart disease (CHD) and other related diseases. The study aimed to identify the causative gene mutations in a Chinese FH family and reveal the pathogenicity and the mechanism of these mutations. Whole exome sequencing was performed in a patient with severe lipid metabolism dysfunction seeking fertility guidance from a Chinese FH family. Two LDLR variants c.1875C > G (p.N625K; novel variant) and c.1448G > A (p.W483*) were identified in the family. Wildtype and mutant LDLR constructs were established by the site-direct mutagenesis technique. Functional studies were carried out by cell transfection to evaluate the impact of detected variants on LDLR activity. The two variants were proven to affect LDL uptake and binding, resulting in cholesterol clearance reduction to different degrees. According to The American College of Medical Genetics and Genomics (ACMG) Standards and Guidelines, the W483* variant was classified as "Pathogenic", while the N625K variant as "VUS". Our results provide novel experimental evidence of functional alteration by LDLR variants identified in our study and expand the mutational spectrum of LDLR mutation induced FH.

Induced alternative splicing an opportunity to study PCSK9 protein isoforms at physiologically relevant concentrations.

Splice modulating antisense oligomers (AOs) are increasingly used to modulate RNA processing. While most are investigated for their use as therapeutics, AOs can also be used for basic research. This study examined their use to investigate internally and terminally truncated proprotein convertase subtilisin/kexin type 9 (PCSK9) protein isoforms. Previous studies have used plasmid or viral-vector-mediated protein overexpression to study different PCSK9 protein isoforms, creating an artificial environment within the cell. Here we designed and tested AOs to remove specific exons that encode for PCSK9 protein domains and produced protein isoforms at more physiologically relevant levels. We evaluated the isoforms' expression, secretion, and subsequent impact on the low-density lipoprotein (LDL) receptor and its activity in Huh-7 cells. We found that modifying the Cis-His-rich domain by targeting exons 10 or 11 negatively affected LDL receptor activity and hence did not enhance LDL uptake although the levels of LDL receptor were increased. On the other hand, removing the hinge region encoded by exon 8, or a portion of the prodomain encoded by exon 2, have the potential as therapeutics for hypercholesterolemia. Our findings expand the understanding of PCSK9 isoforms and their impact on the LDL receptor and its activity at physiologically relevant concentrations.

The LDL receptor is regulated by membrane cholesterol as revealed by fluorescence fluctuation analysis

Membrane cholesterol-rich domains have been shown to be important for regulating a range of membrane protein activities. Low-density lipoprotein receptor (LDLR)-mediated internalization of cholesterol-rich LDL particles is tightly regulated by feedback mechanisms involving intracellular sterol sensors. Since LDLR plays a role in maintaining cellular cholesterol homeostasis, we explore the role that membrane domains may have in regulating LDLR activity. We expressed a fluorescent LDLR-mEGFP construct in HEK293T cells and imaged the unligated receptor or bound to an LDL/DiI fluorescent ligand using total internal reflection fluorescence microscopy. We studied the receptor’s spatiotemporal dynamics using fluorescence fluctuation analysis methods. Image cross correlation spectroscopy reveals a lower LDL-to-LDLR binding fraction when membrane cholesterol concentrations are augmented using cholesterol esterase, and a higher binding fraction when the cells are treated with methyl-β-cyclodextrin) to lower membrane cholesterol. This suggests that LDLR’s ability to metabolize LDL particles is negatively correlated to membrane cholesterol concentrations. We then tested if a change in activity is accompanied by a change in membrane localization. Image mean-square displacement analysis reveals that unligated LDLR-mEGFP and ligated LDLR-mEGFP/LDL-DiI constructs are transiently confined on the cell membrane, and the size of their confinement domains increases with augmented cholesterol concentrations. Receptor diffusion within the domains and their domain-escape probabilities decrease upon treatment with methyl-β-cyclodextrin, consistent with a change in receptor populations to more confined domains, likely clathrin-coated pits. We propose a feedback model to account for regulation of LDLR within the cell membrane: when membrane cholesterol concentrations are high, LDLR is sequestered in cholesterol-rich domains. These LDLR populations are attenuated in their efficacy to bind and internalize LDL. However, when membrane cholesterol levels drop, LDL has a higher binding affinity to its receptor and the LDLR transits to nascent clathrin-coated domains, where it diffuses at a slower rate while awaiting internalization.

Integrated omics approach for the identification of HDL structure-function relationships in PCSK9-related familial hypercholesterolemia

The role of proprotein convertase subtilisin/kexin type 9 (PCSK9) in dyslipidemia may go beyond its immediate effects on low-density lipoprotein receptor (LDL-R) activity. This study aimed to assess PCSK9-derived alterations of high-density lipoprotein (HDL) physiology, which bear a potential to contribute to cardiovascular risk profile. HDL was isolated from 33 patients with familial autosomal dominant hypercholesterolemia (FH), including those carrying PCSK9 gain-of-function (GOF) genetic variants (FH-PCSK9, n=11), together with two groups of dyslipidemic patients employed as controls and carrying genetic variants in the LDL-R not treated (ntFH-LDLR, n=11) and treated (tFH-LDLR, n=11) with statins, and 11 normolipidemic controls. Biological evaluations paralleled by proteomic, lipidomic and glycomic analyses were applied to characterize functional and compositional properties of HDL. Multiple deficiencies in the HDL function were identified in the FH-PCSK9 group relative to dyslipidemic FH-LDLR patients and normolipidemic controls, which involved reduced antioxidative, antiapoptotic, anti-thrombotic and anti-inflammatory activities. By contrast, cellular cholesterol efflux capacity of HDL was unchanged. In addition, multiple alterations of the proteomic, lipidomic and glycomic composition of HDL were found in the FH-PCSK9 group. Remarkably, HDLs from FH-PCSK9 patients were systematically enriched in several lysophospholipids as well as in A2G2S2 (GP13) glycan and apolipoprotein A-IV. Based on network analysis of functional and compositional data, a novel mosaic structure-function model of HDL biology involving FH was developed. Several metrics of anti-atherogenic HDL functionality are altered in FH-PCSK9 patients paralleled by distinct compositional alterations. These data provide a first-ever overview of the impact of GOF PCSK9 genetic variants on structure-function relationships in HDL.

Chrysin 7-O-β-d-glucopyranoside increases hepatic low-density lipoprotein receptor expression through AMP-activated protein kinase activation.

Elevated plasma low-density lipoprotein (LDL) cholesterol level is a risk factor for developing atherosclerosis. Increased LDL receptor (LDLR) expression is expected to reduce the risk of atherosclerotic disease since hepatic LDLR is essential for clearing plasma LDL cholesterol. Here, we screened human LDLR promoter effectors and observed that extracts from peduncles of sweet cherry (Prunus avium) 'Sato-Nishiki' induce LDLR gene promoter activity. We used several analytical and chemical methods to show that chrysin 7-O-β-d-glucopyranoside (chrysin-7G) is one of the compounds that stimulate LDLR gene promoter activity in cherry peduncle extracts. Furthermore, synthetic chrysin-7G increased the expression and activity of LDLR. The chrysin-7G-mediated increase in LDLR expression and activity was completely abolished by treatment with an AMP-activated protein kinase (AMPK) inhibitor, compound C. These results indicate that chrysin-7G increases LDLR expression through AMPK activation and may be a useful compound that can be recycled from waste parts of agricultural products.

MOMAST® Reduces the Plasmatic Lipid Profile and Oxidative Stress and Regulates Cholesterol Metabolism in a Hypercholesterolemic Mouse Model: The Proof of Concept of a Sustainable and Innovative Antioxidant and Hypocholesterolemic Ingredient.

MOMAST® is a patented natural phenolic complex, rich in tyrosol (9.0 g/kg, Tyr), hydroxityrosol (43,5 g/kg, OH-Tyr), and verbascoside (5.0 g/Kg), which is obtained from the OVW by-product of the Coratina cultivar with potent direct antioxidant activity (measured by DPPH and FRAP assays, respectively). Indeed, MOMAST® represents an innovative sustainable bioactive ingredient which has been obtained with ethical and empowering behavior by applying the principles of a circular economy. In the framework of research aimed at fostering its health-promoting activity, in this study it was clearly demonstrated that MOMAST® treatment reduced the oxidative stress and levels of total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol, and increased the HDL levels, without changes in the triglyceride (TG) levels in Western diet (WD)-fed mice. The modulation of the plasmatic lipid profile is similar to red yeast rice (RYR) containing Monacolin K (3%). In addition, at the molecular level in liver homogenates, similarly to RYR, MOMAST® exerts cholesterol-lowering activity through the activation of LDL receptor, whereas, unlike RYR, MOMAST® reduces proprotein convertase subtilisin/kexin type 9 (PCSK9) protein levels via hepatic nuclear factor 1 (HNF1)-α activation. Hence, this study provides the proof of concept regarding the hypocholesterolemic activity of MOMAST, which could be successfully exploited as an active ingredient for the development of innovative and sustainable dietary supplements and functional foods.

GalNAc-Lipid nanoparticles enable non-LDLR dependent hepatic delivery of a CRISPR base editing therapy

Lipid nanoparticles have demonstrated utility in hepatic delivery of a range of therapeutic modalities and typically deliver their cargo via low-density lipoprotein receptor-mediated endocytosis. For patients lacking sufficient low-density lipoprotein receptor activity, such as those with homozygous familial hypercholesterolemia, an alternate strategy is needed. Here we show the use of structure-guided rational design in a series of mouse and non-human primate studies to optimize a GalNAc-Lipid nanoparticle that allows for low-density lipoprotein receptor independent delivery. In low-density lipoprotein receptor-deficient non-human primates administered a CRISPR base editing therapy targeting the ANGPTL3 gene, the introduction of an optimized GalNAc-based asialoglycoprotein receptor ligand to the nanoparticle surface increased liver editing from 5% to 61% with minimal editing in nontargeted tissues. Similar editing was noted in wild-type monkeys, with durable blood ANGPTL3 protein reduction up to 89% six months post dosing. These results suggest that GalNAc-Lipid nanoparticles may effectively deliver to both patients with intact low-density lipoprotein receptor activity as well as those afflicted by homozygous familial hypercholesterolemia.

Hypercholesterolemia induced by spontaneous oligogenic mutations in rhesus macaques (Macaca mulatta).

A rhesus macaque with the fourth highest plasma cholesterol (CH) levels of 501 breeding macaques was identified 22 years ago. Seven offspring with gene mutations causing hypercholesterolemia were obtained. Activity of low-density lipoprotein receptor (LDLR), plasma CH levels and mRNA expression levels of LDLR were measured after administration of 0.1% (0.27 mg/kcal) or 0.3% CH. Activity of p. (Cys82Tyr) of LDLR was 71% and 42% in the heterozygotes and a homozygote, respectively. The mRNA expression level of LDLR in the p. (Val241Ile) of membrane-bound transcription factor protease, site 2 (MBTPS2, S2P protein) was 0.83 times lower than normal levels. LDLR mRNA levels were increased for up to 4 weeks by administration of 0.3% CH before suddenly decreasing to 80% of the baseline levels after 6 weeks. Oligogenic mutations of p. (Cys82Tyr) in LDLR and p. (Val241Ile) in MBTPS2 (S2P) caused hypercholesterolemia exceeding cardiovascular risk levels under a 0.1% CH diet.

How Genetic Variants in Children with Familial Hypercholesterolemia Not Only Guide Detection, but Also Treatment

Familial hypercholesterolemia (FH) is a hereditary disorder that causes severely elevated low-density lipoprotein (LDL-C) levels, which leads to an increased risk for premature cardiovascular disease. A variety of genetic variants can cause FH, namely variants in the genes for the LDL receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9), and/or LDL-receptor adaptor protein 1 (LDLRAP1). Variants can exist in a heterozygous form (HeFH) or the more severe homozygous form (HoFH). If affected individuals are diagnosed early (through screening), they benefit tremendously from early initiation of lipid-lowering therapy, such as statins, and cardiovascular imaging to detect possible atherosclerosis. Over the last years, due to intensive research on the genetic basis of LDL-C metabolism, novel, promising therapies have been developed to reduce LDL-C levels and subsequently reduce cardiovascular risk. Results from studies on therapies focused on inhibiting PCSK9, a protein responsible for degradation of the LDLR, are impressive. As the effect of PCSK9 inhibitors (PCSK9-i) is dependent of residual LDLR activity, this medication is less potent in patients without functional LDLR (e.g., null/null variant). Novel therapies that are expected to become available in the near future focused on inhibition of another major regulatory protein in lipid metabolism (angiopoietin-like 3 (ANGPTL3)) might dramatically reduce the frequency of apheresis in children with HoFH, independently of their residual LDLR. At present, another independent risk factor for premature cardiovascular disease, elevated levels of lipoprotein(a) (Lp(a)), cannot be effectively treated with medication. Further understanding of the genetic basis of Lp(a) metabolism, however, offers a possibility for the development of novel therapies.

Functional Characterization of p.(Arg160Gln) PCSK9 Variant Accidentally Found in a Hypercholesterolemic Subject

Familial hypercholesterolaemia (FH) is an autosomal dominant dyslipidaemia, characterised by elevated LDL cholesterol (LDL-C) levels in the blood. Three main genes are involved in FH diagnosis: LDL receptor (LDLr), Apolipoprotein B (APOB) and Protein convertase subtilisin/kexin type 9 (PCSK9) with genetic mutations that led to reduced plasma LDL-C clearance. To date, several PCSK9 gain-of-function (GOF) variants causing FH have been described based on their increased ability to degrade LDLr. On the other hand, mutations that reduce the activity of PCSK9 on LDLr degradation have been described as loss-of-function (LOF) variants. It is therefore important to functionally characterise PCSK9 variants in order to support the genetic diagnosis of FH. The aim of this work is to functionally characterise the p.(Arg160Gln) PCSK9 variant found in a subject suspected to have FH. Different techniques have been combined to determine efficiency of the autocatalytic cleavage, protein expression, effect of the variant on LDLr activity and affinity of the PCSK9 variant for the LDLr. Expression and processing of the p.(Arg160Gln) variant had a result similar to that of WT PCSK9. The effect of p.(Arg160Gln) PCSK9 on LDLr activity is lower than WT PCSK9, with higher values of LDL internalisation (13%) and p.(Arg160Gln) PCSK9 affinity for the LDLr is lower than WT, EC50 8.6 ± 0.8 and 25.9 ± 0.7, respectively. The p.(Arg160Gln) PCSK9 variant is a LOF PCSK9 whose loss of activity is caused by a displacement of the PCSK9 P' helix, which reduces the stability of the LDLr-PCSK9 complex.

Current Treatment Options in Homozygous Familial Hypercholesterolemia.

Homozygous familial hypercholesterolemia (HoFH) is the rare form of familial hypercholesterolemia causing extremely high low-density lipoprotein cholesterol (LDL-C) levels, leading to atherosclerotic cardiovascular disease (ASCVD) in the first decades of life, if left untreated. Early diagnosis and effective lipid lowering therapy (LLT) are crucial for the prevention of early ASCVD in patients with HoFH. On-treatment LDL-C levels are the best predictor of survival. However, due to the absent or defective LDL-receptor activity, most individuals with HoFH are resistant to conventional LLT, that leads to LDL-C clearance by upregulating LDL-receptors. We are at the dawn of a new era of effective pharmacotherapies for HoFH patients, with new agents providing an LDL-receptor independent cholesterol reduction. In this context, the present review provides a summary of the currently available therapies and emerging therapeutic agents for the management of patients with HoFH, in light of recent evidence and guideline recommendations.

Abstract 10921: Efficacy and Safety of Ongericimab in Chinese Patients With Homozygous Familial Hypercholesterolemia

Background: Homozygous familial hypercholesterolemia (HoFH) is a rare genetic disorder with extremely high low-density lipoprotein cholesterol (LDL-C) levels that contributes to atherosclerotic cardiovascular disease and death, even in adolescent. Ongericimab, a monoclonal antibody against human proprotein convertase subtilisin/kexin type 9 (PCSK9), inhibits PCSK9-mediated degradation of LDL receptor (LDLR), and reduces LDL-C by 58.3-66.5% in Chinese patients with hyperlipidemia. Due to the high genetic heterogeneity of HoFH, the LDL-C lowering effect of Ongericimab remains elusive in Chinese population. This is the first study to assess the efficacy and safety of anti-PCSK9 antibody in Chinese patients with HoFH. Methods: This is a single arm, open-label phase 2 study. 31 patients (aged ≥12 years) with HoFH diagnosed by clinical or genetic criteria, on stable lipid-lowering therapies for ≥4 weeks, were enrolled to receive subcutaneous Ongericimab 450 mg every 4 weeks for 52 weeks. The primary endpoint was percentage change in LDL-C from baseline at week 12. Results: At the time of this interim analysis, 30 out of 31 patients completed 12 weeks treatment. All patients were on statins (77.4% on high intensity statin) and the mean (SD) baseline LDL-C was 8.6 (3.1) mmol/L. The least squares mean percentage change in LDL-C from baseline was -12.6% (95% CI: -19.7%, -5.6%; p=0.001) at week 12. Further analysis based on residual LDLR activity, the mean (SD) LDL-C change from baseline was -21.7 (28.0)% in 14 patients with defective LDLR (at least one defective allele) and -1.4 (9.6)% in 7 patients with negative LDLR (at least one negative allele), respectively (Figure 1). No serious side effects were reported. Conclusion: Ongericimab was well tolerated and significantly reduced LDL-C levels in Chinese patients with HoFH. Patients with defective LDLR demonstrated better response than those with negative LDLR.

Unveiling Compound Heterozygous Familial Hypercholesterolemia

Lead Author's Financial Disclosures Nothing to disclose. Study Funding None. Background/Synopsis A 38-year-old female with a history of hypercholesterolemia as well as a family history of hypercholesterolemia in mother diagnosed at age 68 and in young daughter at age 11 is referred for further evaluation and management of hypercholesterolemia. Objective/Purpose To review the role of genetic testing in management of severe hypercholesterolemia. Methods In addition to routine clinical care, genetic testing was completed by Invitae using gene sequencing and deletion/duplication analysis with next generation sequencing technology (NGS). Results A 38-year-old female has been treated since age 20, when she was first found to have high cholesterol. She is referred for further evaluation after her 11-year-old daughter is noted to have high cholesterol. Invitae Familial Hypercholesterolemia Panel identified a LDLR: c.1027 G>A (p.Gly343Ser) pathogenic variant and LDLR: c.1880 C>T (p.Ala627Val) variant of uncertain significance (VUS). Conclusions Familial hypercholesterolemia (FH) is the most common inherited cardiovascular disease, with a prevalence of 1 in 311, characterized by significantly elevated LDL cholesterol (LDL-C) and responsible for up to 2%-3% of heart attacks in individuals younger than age 60 years. In fact, men with FH who are untreated have a 50% chance of having a coronary event by age 50 and untreated women have a 30% risk by age 60. FH is caused by pathogenic (disease-causing) variants in four major genes: APOB, LDLR, LDLRAP1, PCSK9. The severity of the LDL-C elevation can be determined by the specific variant's impact on LDL-receptor activity and function, and/or the impact from other genes that raise and/or lower the LDL-C. Pathogenic variants in the APOB and PCSK9 and additional LDLR variants may be present as well and are described as double heterozygotes if different genes are affected, compound heterozygotes if different alleles in the same gene are affected, or homozygous if 2 copies of the pathogenic variant is found. In our clinical case, genetic testing revealed a pathogenic variant in the LDLR gene, c.1027 G>A (p.Gly343Ser). This gene is responsible for effective transport of LDL cholesterol into the cell, when defective leads to build up of the un-transported cholesterol in blood vessels. In addition to the pathogenic LDLR variant, a VUS in the LDLR gene, c.1880 C>T (p.Ala627Val) was identified. Variants are of uncertain significance generally do not have evidence to determine pathogenicity with little to no direct impact on phenotype. For now, our patient should be considered heterozygous FH based upon the single pathogenic variant. However, given the supporting evidence and expectation that the VUS is likely pathogenic, we did advise her that the genetic description may change to compound heterozygous depending upon database expansion. Of note, the underrepresentation of this variant in existing databases may reflect sampling bias. Our patient is of Afro-Caribbean (Haitian) heritage, which is a population that has been underrepresented in medical studies. Nothing to disclose.

Unique Case of Management of Severe Hypertriglyceridemia Secondary to Familial Chylomicronemia Syndrome

<h3>Lead Author's Financial Disclosures</h3> Nothing to disclose. <h3>Study Funding</h3> None. <h3>Background/Synopsis</h3> We review a case of a 61-year-old female diagnosed at age 21 with severe hypertriglyceridemia with debilitating, recurrent episodes of acute pancreatitis. <h3>Objective/Purpose</h3> To review a clinical scenario involving severe hypertriglyceridemia and the role of novel therapies in management. <h3>Methods</h3> Clinical management at tertiary care lipid program. <h3>Results</h3> A 61-year-old slightly overweight female with a history of congenital aplasia of the pancreas, coronary artery disease post stents, pre-diabetes, and non-alcoholic fatty liver disease was diagnosed with severe hypertriglyceridemia secondary to chylomicronemia syndrome at age 21. No secondary causes were identified. She was trialed on several cholesterol and triglyceride lowering medications including niacin, rosuvastatin, gemfibrozil, fenofibrate, fish oil supplements with minimal improvement in symptoms and/or reduction in recurrent hospitalizations for acute pancreatitis. Interestingly, she showed a dramatic ∼70% reduction in triglycerides on evinacumab based on compassionate use, resulting in significant improvement in quality of life with no episodes of acute pancreatitis while on therapy for 12 months. <h3>Conclusions</h3> Familial chylomicronemia syndrome (FCS) is an autosomal recessive disorder with a lack of lipoprotein lipase (LPL) functionality, thereby markedly impairing clearance of chylomicrons from the plasma. The primary reason for concern is an increased risk of acute pancreatitis with an estimated odds ratio of 360 in patients with FCS. Acute pancreatitis, in fact, is responsible for a significant economic burden in the United States with an estimated annual cost of care of over $2 billion, accounting for about 50% higher healthcare-related costs compared to patients without acute pancreatitis. Additionally, studies have shown that patients on statin with high residual cardiovascular risk as well as high triglycerides had higher risk for nonfatal myocardial infarction and nonfatal stroke compared to patients with normal triglycerides. Unfortunately, there are currently no FDA-approved treatments for FCS. For this reason, novel therapies are crucially needed to relieve the debilitating state of these patients. One such concept is the use of ANGPTL3 inhibitor, evinacumab, currently FDA approved for homozygous familial hypercholesterolemia. ANGPTL3 inhibition enhances the activities of endothelial lipase and lipoprotein lipase, thereby reducing levels of LDL-C independent of LDL receptor activity, HDL and triglycerides. Based on meta-analysis and a few Phase 1-2 trials, evinacumab is shown to reduce triglycerides from 50% to 80% in patients with severe hypertriglyceridemia. In our patient, with TG/TC ratio >8:1 and normal to low apoB, FCS is more likely the culprit for severe triglyceride burden, contributing to recurrent acute pancreatitis. Furthermore, our patient also suffers from mixed dyslipidemia and metabolic syndrome, which significantly raises her lifetime atherosclerotic cardiovascular risk. Thus, we propose the use of evinacumab in such patients to not only target high triglycerides to reduce risk of acute pancreatitis but also optimize overall cardiovascular risk.

Leu22_Leu23 Duplication at the Signal Peptide of PCSK9 Promotes Intracellular Degradation of LDLr and Autosomal Dominant Hypercholesterolemia.

PCSK9 (Proprotein convertase subtilisin/kexin type 9) regulates LDL-C (low-density lipoprotein cholesterol) metabolism by targeting LDLr (LDL receptor) for lysosomal degradation. PCSK9 gain-of-function variants cause autosomal dominant hypercholesterolemia by reducing LDLr levels, the D374Y variant being the most severe, while loss-of-function variants are associated with low LDL-C levels. Gain-of-function and loss-of-function activities have also been attributed to variants occurring in the PCSK9 signal peptide. Among them, L11 is a very rare PCSK9 variant that seems to increase LDL-C values in a moderate way causing mild hypercholesterolemia. Using molecular biology and biophysics methodologies, activities of L8 and L11 variants, both located in the leucine repetition stretch of the signal peptide, have been extensively characterized in vitro. L8 variant is not associated with increased LDLr activity, whereas L11 activity is increased by ≈20% compared with wt PCSK9. The results suggest that the L11 variant reduces LDLr levels intracellularly by a process resulting from impaired cleavage of the signal peptide. This would lead to less efficient LDLr transport to the cell membrane and promote LDLr intracellular degradation. Deletion of a leucine in the signal peptide in L8 variant does not affect PCSK9 activity, whereas the leucine duplication in the L11 variant enhances LDLr intracellular degradation. These findings highlight the importance of deep in vitro characterization of PCSK9 genetic variants to determine pathogenicity and improve clinical diagnosis and therapy of inherited familial hypercholesterolemia disease.

The two sides of a coin: Pathogenicity and potential therapeutic of LDLRQ722*

AbstractFamilial hypercholesterolemia (FH) is a severe inherited lipid metabolism dysfunction, characterized by high low‐density lipoprotein (LDL) cholesterol levels, mostly due to mutations in the LDL receptor (LDLR) gene. Whole exome sequencing was performed on a consanguineous Chinese FH family and identified a novel homozygous pathogenic mutation LDLR c.C2164T (p. Q722*), forming a novel truncated soluble LDLRQ722*. LDLRQ722* was secreted via the small extracellular vesicles (sEV) and located on the surface of sEV. LDLRQ722*exhibit ∼6% of the wild‐type LDLR activity. sEV containing LDLRQ722* protein reconstructed the lipid metabolism via heparan sulfate proteoglycans (HSPG) and clathrin‐mediated endocytosis. Currently, statins and PCSK9 inhibitors therapy are the mainstay treatment for FH. However, statins and PCSK9 inhibitors substantially vary depending on the residual LDLR activity, while LDLRQ722* reduced circulating LDL‐C levels independently of LDLR residual activity. The study provided new insight into the treatments of FH.

Influence of LDLR pathogenic variants on LDL receptor activity in lymphocytes of patients with Familial Hypercholesterolemia

Influence of LDLR pathogenic variants on LDL receptor activity in lymphocytes of patients with Familial Hypercholesterolemia