Endothelial Lipase Research Articles

Novel roles of PCSK6 in adipose tissue homeostasis

Background and Aims : We have discovered that PCSK6 modulates vascular smooth muscle cell remodeling in atherosclerosis and participates in plaque (in)stability via activation of matrix metalloproteinases, various mitogens and growth factors. In addition, PCSK6 processes two triglyceride lipase family members, endothelial lipase and lipoprotein lipase (LPL) with a possible impact on plasma lipoprotein levels and the adipose tissue. We aimed to investigate the role of PCSK6 in the adipose tissue related lipid metabolism using Pcsk6-/- mice.

Angiopoietin-like 3 (ANGPTL3) resides on HDL and LDL with the latter form having the highest lipase inhibitory activity

Background and Aims : Angiopoietin-like 3 (ANGPTL3) is an inhibitor of lipoprotein lipase (LPL) and endothelial lipase (EL). The impact of ANGPTL3 lowering has been shown to depend on the type of dyslipidemia: reduced LDL cholesterol in patients with familial hypercholesterolemia and reductions in plasma triglycerides in patients with chylomicronemia. This differential effect may be related to a difference in the association of ANGPTL3 with lipoproteins. We therefore hypothesized that ANGPTL3 resides on lipoproteins and that this affects its ability to suppress lipase activity.

Lipases: it's not just pancreatic lipase!

Lipases are water-soluble enzymes that hydrolyze water-insoluble lipid molecules, such as triglycerides, phospholipids, and galactolipids. They are ubiquitous in nature and are present in humans, animals, insects, plants, fungi, and microorganisms. While we commonly consider pancreatic lipase, this review provides an overview of several lipases that are important for the digestion and metabolism of lipids in veterinary species. All of these enzymes have specific functions but share a common α/β-hydrolase fold and a catalytic triad where substrate hydrolysis occurs. The pancreatic lipase gene family is one of the best characterized lipase gene families and consists of 7 mammalian subfamilies: pancreatic lipase, pancreatic lipase related proteins 1 and 2, hepatic lipase, lipoprotein lipase, endothelial lipase, and phosphatidylserine phospholipase A1. Other mammalian lipases that play integral roles in lipid digestion include carboxyl ester lipase and gastric lipase. Although most enzymes have preferred substrate specificity, much overlap occurs across the plethora of lipases because of the similarities in their structures. This has major implications for the development and clinical utilization of diagnostic assays. These implications are further explored in our companion Currents in One Health article by Lim et al in the August 2022 issue of the Journal of American Veterinary Medical Association, which focuses on pancreatic lipase assays for the diagnosis of pancreatitis.

Using Synthetic ApoC-II Peptides and nAngptl4 Fragments to Measure Lipoprotein Lipase Activity in Radiometric and Fluorescent Assays.

Lipoprotein lipase (LPL) plays a crucial role in preventing dyslipidemia by hydrolyzing triglycerides (TGs) in packaged lipoproteins. Since hypertriglyceridemia (HTG) is a major risk factor for cardiovascular disease (CVD), the leading cause of death worldwide, methods that accurately quantify the hydrolytic activity of LPL in clinical and pre-clinical samples are much needed. To date, the methods used to determine LPL activity vary considerably in their approach, in the LPL substrates used, and in the source of LPL activators and inhibitors used to quantify LPL-specific activity, rather than other lipases, e.g., hepatic lipase (HL) or endothelial lipase (EL) activity. Here, we describe methods recently optimized in our laboratory, using a synthetic ApoC-II peptide to activate LPL, and an n-terminal Angiopoietin-Like 4 fragment (nAngptl4) to inhibit LPL, presenting a cost-effective and reproducible method to measure LPL activity in human post-heparin plasma (PHP) and in LPL-enriched heparin released (HR) fractions from LPL secreting cells. We also describe a modified version of the triolein-based assay using human serum as a source of endogenous activators and inhibitors and to determine the relative abundance of circulating factors that regulate LPL activity. Finally, we describe how an ApoC-II peptide and nAngptl4 can be applied to high-throughput measurements of LPL activity using the EnzChek™ fluorescent TG analog substrate with PHP, bovine LPL, and HR LPL enriched fractions. In summary, this manuscript assesses the current methods of measuring LPL activity and makes new recommendations for measuring LPL-mediated hydrolysis in pre-clinical and clinical samples.

Angiopoietin-Like Protein 3 (ANGPTL3) Inhibitors in the Management of Refractory Hypercholesterolemia.

Cardiovascular disease (CVD) is the most common cause of death in a global scale and significantly depends on the elevated plasma levels of low-density lipoprotein cholesterol (LDL-C) and the subsequent formation of atherosclerotic plaques. While physicians have several LDL-C-lowering agents with diverse mechanisms of action, including statins, ezetimibe, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors and inclisiran, angiopoietin-like protein 3 (ANGPTL3) inhibitors have recently emerged as a powerful addition in the armamentarium of lipid-lowering strategies, especially for patients with refractory hypercholesterolemia, as in the case of patients with homozygous familial hypercholesterolemia (HoFH). ANGPTL3 protein is a glycoprotein secreted by liver cells that is implicated in the metabolism of lipids along with other ANGPTL proteins. These proteins inhibit lipoprotein lipase (LPL) and endothelial lipase (EL) in tissues. Loss-of-function mutations affecting the gene encoding ANGPTL3 are linked with lower total cholesterol, LDL-C, and triglyceride (TG) levels. Evinacumab is a monoclonal antibody that targets, binds to, and pharmacologically inhibits ANGPTL3, which was recently approved by the United States Food and Drug Administration (FDA) as a complementary agent to other LDL-C lowering regimens for patients aged 12 or older with HoFH, based on clinical trial evidence that confirmed its safety and efficacy in those patients. Antisense oligonucleotides (ASOs) also represent an interesting class of agents that target and inhibit the mRNA derived from the transcription of ANGPTL3 gene. This review aims to present and discuss the current clinical and scientific data pertaining to the role of ANGPTL3 inhibitors, a novel lipid-modifying class of agents capable of reducing LDL-C levels via a mechanism independent of LDL receptors.

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.

Endothelial lipase: regulation and biological function.

Endothelial lipase is synthetized almost exclusively in endothelial cells and then fixed on the luminal surface of the endothelium by means of heparan sulphate proteoglycans. The enzyme is expressed in the endothelium of nearly all tissues and the degree of expression is higher in richly vascularized tissues than in the less vascularized ones. The endothelial lipase expression in tissues is upregulated by shear and cyclic stress, angiotensin II and hypertension. The plasma enzyme level is elevated by pro-inflammatory cytokines, in metabolic syndrome and obesity. Prolonged exercise reduces the plasma enzyme level in the rat. The activity of the enzyme is inhibited by: sphingomyelin, angiopoietin-like protein 3 and 4, and insulin. Endothelial lipase reduces the plasma high density lipoprotein concentration and changes its properties. The enzyme is considered to be the main regulator of the plasma high density lipoprotein concentration. The plasma endothelial lipase concentration is elevated in coronary atherosclerosis and it is inversely correlated with the plasma high density lipoprotein level. The enzyme is considered to exert mostly pro-atherogenic effects. Its action as triglyceride lipase is important in hypertriglyceridemia.

Whole Transcriptome Profiling of the Effects of Cadmium on the Liver of the Xiangxi Yellow Heifer.

Cadmium (Cd) is a major heavy metal toxicant found in industrial zones. Humans and animals are exposed to it through their diet, which results in various physiological problems. In the current study, the toxic effects of Cd on the liver were investigated by whole-transcriptome sequencing (RNA-seq) of the livers of Xiangxi heifers fed a diet with excess Cd. We randomly divided six healthy heifers into two groups. The first group received a control diet, whereas the second group received Cd-exceeding diets for 100 days. After 100 days, the livers were collected. A total of 551 differentially expressed mRNAs, 24 differentially expressed miRNAs, and 169 differentially expressed lncRNAs were identified (p < 0.05, |log2FC| >1). Differentially expressed genes (DEGs) were analyzed by gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. We found that under Cd exposure, DEGs were enriched in the adenosine 5'-monophosphate–activated protein kinase pathway, which is involved in autophagy regulation, and the peroxisome proliferator–activated receptor pathway, which is involved in lipid metabolism. In addition, the apolipoprotein A4 gene, which has anti-inflammatory and antioxidant effects, the anti-apoptotic gene ATPase H+/K+ transporting the nongastric alpha2 subunit, and the cholesterol metabolism–associated gene endothelial lipase gene were significantly downregulated. C–X–C motif chemokine ligand 3, cholesterol 7α-hydroxylase, and stearoyl-CoA desaturase, which are involved in the development of fatty liver, were significantly upregulated. These genes revealed the main effects of Cd on the liver of Xiangxi yellow heifers. The current study provides insightful information regarding the DEGs involved in autophagy regulation, apoptosis, lipid metabolism, anti-inflammation, and antioxidant enzyme activity. These may serve as useful biomarkers for predicting and treating Cd-related diseases in the future.

Role of Endothelial Cell Lipoprotein Lipase for Brown Adipose Tissue Lipid and Glucose Handling.

Cold-induced activation of brown adipose tissue (BAT) has an important impact on systemic lipoprotein metabolism by accelerating the processing of circulating triglyceride-rich lipoproteins (TRL). Lipoprotein lipase (LPL) expressed by adipocytes is translocated via endothelial to the capillary lumen, where LPL acts as the central enzyme for the vascular lipoprotein processing. Based on preliminary data showing that LPL is not only expressed in adipocytes but also in endothelial cells of cold-activated BAT, we aimed to dissect the relevance of endothelial versus adipocyte LPL for lipid and energy metabolism in the context of adaptive thermogenesis. By metabolic studies we found that cold-induced triglyceride uptake into BAT, lipoprotein disposal, glucose uptake and adaptive thermogenesis were not impaired in mice lacking Lpl exclusively in endothelial cells. This finding may be explained by a compensatory upregulation in the expression of adipocyte-derived Lpl and endothelial lipase (Lipg).

Sphingosine-1-phosphate: metabolism, transport, atheroprotection and effect of statin treatment.

To better define the metabolism of sphingosine-1-phosphate (S1P), its transport in plasma and its interactions with S1P receptors on vascular cells, and to evaluate the effect of statin treatment on the subnormal plasma levels of high-density lipoprotein (HDL)-bound S1P characteristic of the atherogenic dyslipidemia of metabolic syndrome (MetS). Neither clinical intervention trials targeted to raising high-density lipoprotein-cholesterol (HDL-C) levels nor human genome-wide association studies (GWAS) studies have provided evidence to support an atheroprotective role of HDL. Recently however a large monogenic univariable Mendelian randomization on the N396S mutation in the gene encoding endothelial lipase revealed a causal protective effect of elevated HDL-C on coronary artery disease conferred by reduced enzyme activity. Given the complexity of the HDL lipidome and proteome, components of HDL other than cholesterol may in all likelihood contribute to such a protective effect. Among HDL lipids, S1P is a bioactive sphingolipid present in a small proportion of HDL particles (about 5%); indeed, S1P is preferentially enriched in small dense HDL3. As S1P is bound to apolipoprotein (apo) M in HDL, such enrichment is consistent with the elevated apoM concentration in HDL3. When HDL/apoM-bound S1P acts on S1P1 or S1P3 receptors in endothelial cells, potent antiatherogenic and vasculoprotective effects are exerted; those exerted by albumin-bound S1P at these receptors are typically weaker. When HDL/apoM-bound S1P binds to S1P2 receptors, proatherogenic effects may potentially be induced. Subnormal plasma levels of HDL-associated S1P are typical of dyslipidemic individuals at high cardiovascular risk and in patients with coronary heart disease. International Guidelines recommend statin treatment as first-line lipid lowering therapy in these groups. The cardiovascular benefits of statin therapy are derived primarily from reduction in low-density lipoprotein (LDL)-cholesterol, although minor contributions from pleiotropic actions cannot be excluded. Might statin treatment therefore normalize, directly or indirectly, the subnormal levels of S1P in dyslipidemic subjects at high cardiovascular risk? Our unpublished findings in the CAPITAIN study (ClinicalTrials.gov: NCT01595828), involving a cohort of obese, hypertriglyceridemic subjects (n = 12) exhibiting the MetS, showed that pitavastatin calcium (4 mg/day) treatment for 180days was without effect on either total plasma or HDL-associated S1P levels, suggesting that statin-mediated improvement of endothelial function is not due to normalization of HDL-bound S1P. Statins may however induce the expression of S1P1 receptors in endothelial cells, thereby potentiating increase in endothelial nitric oxide synthase response to HDL-bound S1P, with beneficial downstream vasculoprotective effects. Current evidence indicates that S1P in small dense HDL3 containing apoM exerts antiatherogenic effects and that statins exert vasculoprotective effects through activation of endothelial cell S1P1 receptors in response to HDL/apoM-bound S1P.

Comparative chemoreactomic analysis of ornithine aspartate, S-ademethionine and ursodeoxycholic acid

Purpose of the study. The pharmacological effects of ornithine are primarily due to its participation in the neutralization of ammonia and in the metabolism of amino acids. To clarify the mechanisms of action of ornithine, a chemoreactom analysis of ornithine aspartate was performed in comparison with S-ademetionine (S-AM) and ursodeoxycholic acid (UDCA). Methods. The effects of the investigated substances on the metabolism of urates (derivatives of uric acid), vasoactivity, vascular structure and cytoprotection were assessed by the method of chemoreactome analysis. Results. It was found that a decrease in blood urate levels is associated with inhibition by ornithine of the urate transporter URAT1 (ornithine – IC50 = 65 nM, S-AM – 1060 nM, UDCA – 94 nM) and xanthine oxidase (ornithine – IC50 = 910 nM, other molecules IC50 = 9655-11040 nM). Among the studied molecules, ornithine was distinguished by the most pronounced vasodilatory properties (probably associated with inhibition of adrenergic receptors: Kd = 35 nM, other molecules – 1108-1428 nM). The highest antidyslipidemic activity was also shown for ornithine (9.4 %) and S-AM (10.2 %), the lowest for UDCA (4.6 %). The antidyslipidemic effect of ornithine is associated with inhibition of endothelial lipase (IC50 = 258 nM for ornithine). The cytoprotective effects of ornithine are associated with an increase in glutathione synthesis, a decrease in the glutamatergic activity of neurons under conditions of glutamate stress, inhibition of prostaglandin D-synthase, and a decrease in the intensity of acute lymphocytic inflammation without immunosuppression. Conclusion. Thus, the results of the ornithine chemoreactom analysis indicate a significant expansion of the spectrum of the pharmacological effects of ornithine, including not only hepatoprotection, but also cardioprotection and nephroprotection.

Impact of Sepsis on High-Density Lipoprotein Metabolism.

Background: High-density lipoproteins (HDL) are thought to play a protective role in sepsis through several mechanisms, such as promotion of steroid synthesis, clearing bacterial toxins, protection of the endothelial barrier, and antioxidant/inflammatory activities. However, HDL levels decline rapidly during sepsis, but the contributing mechanisms are poorly understood. Methods/Aim: In the present study, we investigated enzymes involved in lipoprotein metabolism in sepsis and non-sepsis patients admitted to the intensive care unit (ICU). Results: In 53 ICU sepsis and 25 ICU non-sepsis patients, we observed significant differences in several enzymes involved in lipoprotein metabolism. Lecithin-cholesterol acyl transferase (LCAT) activity, LCAT concentration, and cholesteryl transfer protein (CETP) activity were significantly lower, whereas phospholipid transfer activity protein (PLTP) and endothelial lipase (EL) were significantly higher in sepsis patients compared to non-sepsis patients. In addition, serum amyloid A (SAA) levels were increased 10-fold in sepsis patients compared with non-sepsis patients. Furthermore, we found that LCAT activity was significantly associated with ICU and 28-day mortality whereas SAA levels, representing a strong inflammatory marker, did not associate with mortality outcomes. Conclusion: We provide novel data on the rapid and robust changes in HDL metabolism during sepsis. Our results clearly highlight the critical role of specific metabolic pathways and enzymes in sepsis pathophysiology that may lead to novel therapeutics.

Endothelial lipase promotes acute myeloid leukemia progression through metabolic reprogramming.

Metabolic reprogramming occurs in the clonal evolution of acute myeloid leukemia (AML), which contributes to cell survival under metabolic stress and the development of drug resistance. Leukemic cells exhibit various metabolic profiles, which involve multiple metabolic pathways due to the heterogeneity of AML. However, studies on metabolic targets for AML treatment are mostly focused on glycolysis at present. In this work, we established conditional knock-in AML mouse models harboring Dnmt3aR878H/WT, NrasG12D/WT, and both of the mutations, respectively. Transcriptomic analysis of Gr1+ cells from bone marrow was performed afterward to screen interested metabolic pathways and target genes. Candidate genes were studied using the CRISPR/Cas9 technique, quantitative real-time RT-PCR, and flow cytometric analyses. We revealed that multiple metabolic pathways were affected in AML mice, including lipid metabolism. Endothelial lipase (LIPG) was obviously upregulated in leukemic cells from AML mice with Dnmt3a mutation. We performed knockout of LIPG in OCI-AML3 cells carrying DNMT3A R882C mutation by using the CRISPR/Cas9 technique. Depletion of LIPG led to proliferation inhibition, apoptosis, damage of antioxidant capacity, and myeloid differentiation in OCI-AML3 cells. LIPG might serve as a potential metabolic target for the treatment of AML with abnormal lipid metabolism.

The Potential of ANGPTL8 Antagonism to Simultaneously Reduce Triglyceride and Increase HDL-Cholesterol Plasma Levels.

Elevated triglyceride (TG) and reduced high-density lipoprotein-cholesterol (HDL-C) plasma levels are risk factors for atherosclerosis and cardiovascular disease. Therefore, a drug that simultaneously reduces TG and increases HDL-C plasma levels has the potential to prevent and treat these diseases. Angiopoietin-like 3 (ANGPTL3) regulates plasma TG and HDL-C levels by inhibiting lipoprotein lipase (LPL) and endothelial lipase (EL), respectively. ANGPTL3 inhibition of LPL requires complex formation with ANGPTL8, which is not required for its inhibition of EL. Therefore, the entire pool of plasma ANGPTL3 can be classified as ANGPTL8-associated ANGPTL3 and ANGPTL8-free ANGPTL3, where the former inhibits LPL and the latter inhibits EL. ANGPTL8 antibodies or inhibitors that block its interactions with ANGPTL3 can disrupt or preclude the ANGPTL3-8 complex formation, resulting in fewer ANGPTL3-8 complexes (reduced LPL inhibition), but more free ANGPTL3 (enhanced EL inhibition). Therefore, ANGPTL8 antagonism increases LPL activity while decreasing EL activity, thus leading to reduced plasma TG while simultaneously increasing HDL-C levels. In humans, carriers of ANGPTL8 truncating variants consistently have lower TG but higher HDL-C levels, supporting this hypothesis.

Abstract 12054: Evinacumab Reduces Atherogenic Lipids and Apolipoprotein B in Patients With Severe Hypertriglyceridemia

Background: Hypertriglyceridemia (HTG) is the consequence of elevated triglyceride-rich lipoproteins (TGRLs) containing apolipoprotein B (apoB), such as VLDL and chylomicrons. Epidemiological and genetic studies indicate that triglycerides (TGs) and the cholesterol within TGRLs causally contribute to coronary heart disease risk (CHD). Evinacumab (EVIN), an angiopoietin-like 3 inhibitor, lowers TGs by derepressing lipoprotein lipase (LPL) and endothelial lipase activity. In a Phase 2 trial in patients (pts) with severe HTG (sHTG, fasting TGs ≥500 mg/dL), EVIN was previously shown to reduce TGs in patients (pts) without familial chylomicronemia syndrome (FCS) and to be generally well tolerated (NCT03452228). This post-hoc analysis reports further details on the efficacy of EVIN in reducing atherogenic lipids/lipoproteins. Methods: Pts (N=51) were treated and assigned to cohorts based on genotype: Cohort 1 (n=17), FCS pts with bi-allelic loss-of-function (LOF) LPL pathway mutations; Cohort 2 (n=15), multifactorial chylomicronemia syndrome (MCS) pts with heterozygous LOF LPL pathway mutations; Cohort 3 (n=19), MCS pts without LPL pathway mutations. Pts were randomized (2:1) to IV EVIN 15 mg/kg or placebo every 4 weeks over a 12-week double-blind treatment (tx) period (DBTP), followed by a 12-week single-blind tx period where all pts received EVIN. Results: Of 51 pts with sHTG treated in the DBTP, 70.6% were categorized as high cardiovascular risk, and 21.6% had a history of CHD. In non-FCS pts (Cohorts 2 and 3), in addition to reducing TGs, EVIN reduced atherogenic lipids and apolipoproteins at Week (W) 12 compared with baseline (Table), including non-HDL-C, remnant cholesterol, and apoB (including apoB100 and apoB48). Overall, reductions observed at W12 were maintained through W24. Conclusions: In this post-hoc analysis, EVIN reduced atherogenic lipids and apoB, indicating it may have the potential to reduce CHD risk in pts with sHTG without genetic FCS.

Transcriptomic therapy for dyslipidemias utilizing nucleic acids targeted at ANGPTL3.

Angiopoietin-like protein 3 (ANGPTL3) is a key physiological regulator of plasma lipid and lipoproteinmetabolism that involves the control of enzymes, lipoprotein and endothelial lipases. Inhibition of ANGPTL3 offers a new approach for correcting the health risks of dyslipidemia, including familial hypercholesterolemia, mixed hyperlipidemia, metabolic syndromeand/or severe hypertriglyceridemia. ANGPTL3 inhibition with nucleic acid-based antisense oligonucleotide and siRNA can correct dyslipidemia chiefly by reducing production and increasing catabolism of triglyceride-rich lipoprotein and LDL particles. Early clinical trials have demonstrated that these agents can safely and effectively lower plasma triglyceride and LDL-cholesterol levels by up to 70and 50%, respectively. However, the long-term safety and cost-effectiveness of these agents await to be confirmed in anongoing and future clinical trials.

Endothelial lipase mediates efficient lipolysis of triglyceride-rich lipoproteins.

Triglyceride-rich lipoproteins (TRLs) are circulating reservoirs of fatty acids used as vital energy sources for peripheral tissues. Lipoprotein lipase (LPL) is a predominant enzyme mediating triglyceride (TG) lipolysis and TRL clearance to provide fatty acids to tissues in animals. Physiological and human genetic evidence support a primary role for LPL in hydrolyzing TRL TGs. We hypothesized that endothelial lipase (EL), another extracellular lipase that primarily hydrolyzes lipoprotein phospholipids may also contribute to TRL metabolism. To explore this, we studied the impact of genetic EL loss-of-function on TRL metabolism in humans and mice. Humans carrying a loss-of-function missense variant in LIPG, p.Asn396Ser (rs77960347), demonstrated elevated plasma TGs and elevated phospholipids in TRLs, among other lipoprotein classes. Mice with germline EL deficiency challenged with excess dietary TG through refeeding or a high-fat diet exhibited elevated TGs, delayed dietary TRL clearance, and impaired TRL TG lipolysis in vivo that was rescued by EL reconstitution in the liver. Lipidomic analyses of postprandial plasma from high-fat fed Lipg-/- mice demonstrated accumulation of phospholipids and TGs harboring long-chain polyunsaturated fatty acids (PUFAs), known substrates for EL lipolysis. In vitro and in vivo, EL and LPL together promoted greater TG lipolysis than either extracellular lipase alone. Our data positions EL as a key collaborator of LPL to mediate efficient lipolysis of TRLs in humans and mice.

Angiopoietin-like protein 4 (ANGPTL4) is an inhibitor of endothelial lipase (EL) while the ANGPTL4/8 complex has reduced EL-inhibitory activity

We previously demonstrated that angiopoietin-like protein 8 (ANGPTL8) forms ANGPTL3/8 and ANGPTL4/8 complexes that increase with feeding to direct fatty acids (FA) toward adipose tissue through differential modulation of lipoprotein lipase (LPL) activity. Each complex correlated inversely with high density lipoprotein cholesterol (HDL) in control subjects. We thus investigated ANGPTL3/8 and ANGPTL4/8 levels in type 2 diabetes patients, who can present with decreased HDL. While ANGPTL3/8 levels in type 2 diabetes patients were similar to those previously observed in normal controls, ANGPTL4/8 levels were roughly twice as high as those in control subjects. Concentrations of ANGPTL3/8 and ANGPTL4/8 in type 2 diabetes patients were inversely correlated with HDL, with the correlation being significant for ANGPTL4/8. We therefore measured the ability of the various ANGPTL proteins and complexes to inhibit endothelial lipase (EL), the enzyme which hydrolyzes phospholipids (PL) in HDL. While confirming ANGPTL3 as an EL inhibitor, we found that ANGPTL4 was a more potent EL inhibitor than ANGPTL3. Interestingly, we observed that while ANGPTL3/8 had increased EL-inhibitory activity compared to ANGPTL3 alone, ANGPTL4/8 exhibited decreased potency in inhibiting EL compared to ANGPTL4 alone. Together, these results show for the first time that ANGPTL4 is a more potent EL inhibitor than ANGPTL3 and suggest a possible reason for why ANGPTL4/8 levels are correlated inversely with HDL.

Dairy Processing Affects the Gut Digestion and Microecology by Changing the Structure and Composition of Milk Fat Globules.

Milk fat globules (MFGs) are the major source of energy for infants' dietary intake. In this study, the effects of changes in the structure and composition of MFG after dairy processing on lipolysis and immune regulation were investigated. Pasteurized MFG tends to form protein aggregates to prevent lipolysis. However, the aggregate is rich in neutrophil degranulation products, which are effective in killing pathogens. Homogenized MFG has the lowest hydrolysis rate due to the reconstituted anti-lipase barrier and exposed apolipoprotein. Simultaneously, the reconstituted barrier can compensate for the lack of the complement cascade. Spray-dried MFG had the highest hydrolysis rate attributable to the disrupted MFG barrier and the release of lipoprotein lipase and endothelial lipase. The immunomodulatory properties of spray-dried MFG proteins are mainly mediated by the toll-like receptor (TLR) signaling pathway. This research provides the improvement basis of dairy processing and functional infant formulas.

AAV5-based gene therapy targeting ANGPTL3 reduces hyperlipidemia and development of atherosclerosis in APOE*3-Leiden.CETP mice

Background and Aims: ANGPTL3 is an inhibitor of lipoprotein and endothelial lipase, thus restricting triglyceride hydrolysis from triglyceride-rich lipoproteins and leading to increased plasma lipid levels. We explored the therapeutic potential of a gene therapeutic approach to target ANGPTL3 expression by introduction of an artificial microRNA into hepatocytes using an adeno-associated virus type 5 (AAV5) vector (AAV5-miQURE™) in hyperlipidemic APOE*3-Leiden.CETP mice, alone or in combination with atorvastatin treatment.