A dual apolipoprotein C-II mimetic-apolipoprotein C-III antagonist peptide lowers plasma triglycerides

An overview of persistent chylomicronemia: much more than meets the eye

PURPOSE OF REVIEW

The aim of this review is to provide an overview of severe hypertriglyceridemia presenting in the form of chylomicronemia that persists despite treatment of secondary causes and the use of conventional lipid-lowering treatment.

RECENT FINDINGS

Persistent chylomicronemia is a rare syndromic disorder that affects carriers of bi-allelic combinations of pathogenic gene variants impairing lipoprotein lipase (LPL) activity, as well as a significant number of individuals who do not meet this genetic criterion. It is associated with a high risk of acute pancreatitis and other morbidities. Effective innovative treatments for severe hypertriglyceridemia are being developed and are becoming available. Patients with persistent chylomicronemia of any cause respond equally to next-generation therapies with LPL-independent mechanisms of action and do not generally respond to conventional LPL-dependent treatments.

SUMMARY

Not all individuals with persistent chylomicronemia carry a proven pathogenic combination of gene variants that impair LPL activity. Documenting the clinical characteristics of people with persistent chylomicronemia and their response to emerging therapies is essential to correctly establish their risk trajectory and ensure equitable access to personalized treatment.

Use of Nigella sativa silver nanocomposite as an alternative therapy against thioacetamide nephrotoxicity

Nigella sativa (N. sativa) L. (Ranunculaceae), commonly referred to as black cumin, has a long history of usage as an herbal remedy. It has been utilized conventionally and in clinical settings to treat various illnesses. Six groups of male Wister rats were randomly selected as Gp I, represented as control; Gp II administered N. sativa aqueous extract (NSAE); 200 mg/kg/d, Gp III received N. sativa silver nanocomposite (NS-Ag-NC); 0.25 mg/kg/d; Gp IV administered thioacetamide (TAA);100 mg/kg; thrice weekly and Gps V and VI administered NSAE and NS-Ag-NC with TAA for six weeks, respectively. Findings showed that GC-MS analysis of NSAE has a high concentration of phytochemicals with strong antioxidant activity. Results revealed that TAA administration elevated TBARS, H2O2, PCC, NO levels, kidney function parameters, LDH activity, and up-regulated TNF-α, IL-1β, NF-kβ, and COX-2 gene expressions. In contrast, enzymatic and non-enzymatic antioxidants and ALP activity were extensively diminished. Also, severe abnormalities in lipid profile, hematological parameters, and histopathological features were noted. On the other hand, the administration of NSAE or NS-Ag-NC followed by TAA intoxication reduces renal impairment, restores the antioxidant system, and downregulates the expression of TNF-α, IL-1β, NF-kβ, and COX-2 genes in rats' renal tissues. Collectively, NS-Ag-NC has more prevalent nephroprotective impacts than NSAE and can adjust the oxidant/antioxidant pathways besides their anti-inflammatory efficacy against TAA toxicity.

Long-term clinical outcomes and management of hypertriglyceridemia in children with Apo-CII deficiency

BACKGROUND AND AIM

APO CII, one of several cofactors which regulate lipoprotein lipase enzyme activity, plays an essential role in lipid metabolism. Deficiency of APO CII is an ultra-rare autosomal recessive cause of familial chylomicronemia syndrome. We present the long-term clinical outcomes of 12 children with APO CII deficiency.

METHODS AND RESULTS

The data of children with genetically confirmed APO CII deficiency were evaluated retrospectively. Twelve children (8 females) with a mean follow-up of 10.1 years (±3.9) were included. At diagnosis, the median age was 60 days (13 days-10 years). Initial clinical findings included lipemic serum (41.6%), abdominal pain (41.6%), and vomiting (16.6%). At presentation, the median triglyceride (TG) value was 4341 mg/dL (range 1277-14,110). All patients were treated with a restricted fat diet, medium-chain triglyceride (MCT), and omega-3-fatty acids. In addition, seven patients (58.3%) received fibrate. Fibrate was discontinued in two patients due to rhabdomyolysis and in one patient because of cholelithiasis. Seven (58.3%) patients experienced pancreatitis during the follow-up period. One female experienced recurrent pancreatitis and was treated with fresh frozen plasma (FFP).

CONCLUSIONS

Apo CII deficiency is an ultra-rare autosomal recessive condition of hypertriglyceridemia associated with significant morbidity and mortality. Low-fat diet and MCT supplementation are the mainstays of therapy, while the benefit of TG-lowering agents are less well-defined.

APOA1/C3/A4/A5 Gene Cluster at 11q23.3 and Lipid Metabolism Disorders: From Epigenetic Mechanisms to Clinical Practices

The APOA1/C3/A4/A5 cluster is an essential component in regulating lipoprotein metabolism and maintaining plasma lipid homeostasis. A genome-wide association analysis and Mendelian randomization have revealed potential associations between genetic variants within this cluster and lipid metabolism disorders, including hyperlipidemia and cardiovascular events. An enhanced understanding of the complexity of gene regulation has led to growing recognition regarding the role of epigenetic variation in modulating APOA1/C3/A4/A5 gene expression. Intensive research into the epigenetic regulatory patterns of the APOA1/C3/A4/A5 cluster will help increase our understanding of the pathogenesis of lipid metabolism disorders and facilitate the development of new therapeutic approaches. This review discusses the biology of how the APOA1/C3/A4/A5 cluster affects circulating lipoproteins and the current progress in the epigenetic regulation of the APOA1/C3/A4/A5 cluster.

Genetic Association between Lipid-Regulating Drug Targets and Diabetic Retinopathy: A Drug Target Mendelian Randomization Study

Background

Diabetic retinopathy (DR) is a diabetic microvascular complication and a leading cause of vision loss. However, there is a lack of effective strategies to reduce the risk of DR currently. The present study is aimed at assessing the causal effect of lipid-regulating targets on DR risk using a two-sample Mendelian randomization (MR) study.

Method

Genetic variants within or near drug target genes, including eight lipid-regulating targets for LDL-C (HMGCR, PCSK9, and NPC1L1), HDL-C (CETP, SCARB1, and PPARG), and TG (PPARA and LPL), were selected as exposures. The exposure data were obtained from the IEU OpenGWAS project. The outcome dataset related to DR was obtained from the FinnGen research project. Inverse-variance-weighted MR (IVW-MR) was used to calculate the effect estimates by each target. Sensitivity analyses were performed to verify the robustness of the results.

Results

There was suggestive evidence that PCSK9-mediated LDL-C levels were positively associated with DR, with OR (95% CI) of 1.34 (1.02-1.77). No significant association was found between the expression of HMGCR- and NPC1L1-mediated LDL-C levels; CETP-, SCARB1-, and PPARG-mediated HDL-C levels; PPARA- and LPL-mediated TG levels; and DR risk.

Conclusions

This is the first study to reveal a genetically causal relationship between lipid-regulating drug targets and DR risk. PCSK9-mediated LDL-C levels maybe positively associated with DR risk at the genetic level. This study provides suggestive evidence that PCSK9 inhibition may reduce the risk of DR.

Targeting host-specific metabolic pathways-opportunities and challenges for anti-infective therapy

Microorganisms can takeover critical metabolic pathways in host cells to fuel their replication. This interaction provides an opportunity to target host metabolic pathways, in addition to the pathogen-specific ones, in the development of antimicrobials. Host-directed therapy (HDT) is an emerging strategy of anti-infective therapy, which targets host cell metabolism utilized by facultative and obligate intracellular pathogens for entry, replication, egress or persistence of infected host cells. This review provides an overview of the host lipid metabolism and links it to the challenges in the development of HDTs for viral and bacterial infections, where pathogens are using important for the host lipid enzymes, or producing their own analogous of lecithin-cholesterol acyltransferase (LCAT) and lipoprotein lipase (LPL) thus interfering with the human host's lipid metabolism.

Exploring apolipoprotein C-III: pathophysiological and pharmacological relevance

The availability of pharmacological approaches able to effectively reduce circulating LDL cholesterol (LDL-C) has led to a substantial reduction in the risk of atherosclerosis-related cardiovascular disease (CVD). However, a residual cardiovascular (CV) risk persists in treated individuals with optimal levels of LDL-C. Additional risk factors beyond LDL-C are involved, and among these, elevated levels of triglycerides (TGs) and TG-rich lipoproteins are causally associated with an increased CV risk. Apolipoprotein C-III (apoC-III) is a key regulator of TG metabolism and hence circulating levels through several mechanisms including the inhibition of lipoprotein lipase activity and alterations in the affinity of apoC-III-containing lipoproteins for both the hepatic receptors involved in their removal and extracellular matrix in the arterial wall. Genetic studies have clarified the role of apoC-III in humans, establishing a causal link with CVD and showing that loss-of-function mutations in the APOC3 gene are associated with reduced TG levels and reduced risk of coronary heart disease. Currently available hypolipidaemic drugs can reduce TG levels, although to a limited extent. Substantial reductions in TG levels can be obtained with new drugs that target specifically apoC-III; these include two antisense oligonucleotides, one small interfering RNA and an antibody.

Understanding Hypertriglyceridemia: Integrating Genetic Insights

Hypertriglyceridemia is an exceptionally complex metabolic disorder characterized by elevated plasma triglycerides associated with an increased risk of acute pancreatitis and cardiovascular diseases such as coronary artery disease. Its phenotype expression is widely heterogeneous and heavily influenced by conditions as obesity, alcohol consumption, or metabolic syndromes. Looking into the genetic underpinnings of hypertriglyceridemia, this review focuses on the genetic variants in LPL, APOA5, APOC2, GPIHBP1 and LMF1 triglyceride-regulating genes reportedly associated with abnormal genetic transcription and the translation of proteins participating in triglyceride-rich lipoprotein metabolism. Hypertriglyceridemia resulting from such genetic abnormalities can be categorized as monogenic or polygenic. Monogenic hypertriglyceridemia, also known as familial chylomicronemia syndrome, is caused by homozygous or compound heterozygous pathogenic variants in the five canonical genes. Polygenic hypertriglyceridemia, also known as multifactorial chylomicronemia syndrome in extreme cases of hypertriglyceridemia, is caused by heterozygous pathogenic genetic variants with variable penetrance affecting the canonical genes, and a set of common non-pathogenic genetic variants (polymorphisms, using the former nomenclature) with well-established association with elevated triglyceride levels. We further address recent progress in triglyceride-lowering treatments. Understanding the genetic basis of hypertriglyceridemia opens new translational opportunities in the scope of genetic screening and the development of novel therapies.

The chylomicron saga: time to focus on postprandial metabolism

Since statins have had such tremendous therapeutic success over the last three decades, the field of atherosclerosis has become somewhat LDL-centric, dismissing the relevance of triglycerides (TG), particularly chylomicrons, in atherogenesis. Nonetheless, 50% of patients who take statins are at risk of developing atherosclerotic cardiovascular disease (ASCVD) and are unable to achieve their goal LDL-C levels. This residual risk is mediated, in part by triglyceride rich lipoproteins (TRL) and their remnants. Following his seminal investigation on the subject, Zilversmit proposed that atherosclerosis is a postprandial event in 1979 (1-4). In essence, the concept suggests that remnant cholesterol-rich chylomicron (CM) and very-low density lipoprotein (VLDL) particles play a role in atherogenesis. Given the foregoing, this narrative review addresses the most recent improvements in our understanding of postprandial dyslipidemia. The primary metabolic pathways of chylomicrons are discussed, emphasizing the critical physiological role of lipoprotein lipase and apoCIII, the importance of these particles' fluxes in the postprandial period, their catabolic rate, the complexities of testing postprandial metabolism, and the role of angiopoietin-like proteins in the partition of CM during the fed cycle. The narrative is rounded out by the dysregulation of postprandial lipid metabolism in insulin resistance states and consequent CVD risk, the clinical evaluation of postprandial dyslipidemia, current research limits, and potential future study directions.

Unlocking the mysteries of VLDL: exploring its production, intracellular trafficking, and metabolism as therapeutic targets

Reducing circulating lipid levels is the centerpiece of strategies for preventing and treating atherosclerotic cardiovascular disease (ASCVD). Despite many available lipid-lowering medications, a substantial residual cardiovascular risk remains. Current clinical guidelines focus on plasma levels of low-density lipoprotein (LDL). Recent attention has been given to very low-density lipoprotein (VLDL), the precursor to LDL, and its role in the development of coronary atherosclerosis. Preclinical investigations have revealed that interventions targeting VLDL production or promoting VLDL metabolism, independent of the LDL receptor, can potentially decrease cholesterol levels and provide therapeutic benefits. Currently, methods, such as mipomersen, lomitapide, and ANGPTL3 inhibitors, are used to reduce plasma cholesterol and triglyceride levels by regulating the lipidation, secretion, and metabolism of VLDL. Targeting VLDL represents an avenue for new lipid-lowering strategies. Interventions aimed at reducing VLDL production or enhancing VLDL metabolism, independent of the LDL receptor, hold promise for lowering cholesterol levels and providing therapeutic benefits beyond LDL in the management of ASCVD.

Macromolecular Interactions of Lipoprotein Lipase (LPL)

Lipoprotein lipase (LPL) is a critical enzyme in humans that provides fuel to peripheral tissues. LPL hydrolyzes triglycerides from the cores of lipoproteins that are circulating in plasma and interacts with receptors to mediate lipoprotein uptake, thus directing lipid distribution via catalytic and non-catalytic functions. Functional losses in LPL or any of its myriad of regulators alter lipid homeostasis and potentially affect the risk of developing cardiovascular disease-either increasing or decreasing the risk depending on the mutated protein. The extensive LPL regulatory network tunes LPL activity to allocate fatty acids according to the energetic needs of the organism and thus is nutritionally responsive and tissue dependent. Multiple pharmaceuticals in development manipulate or mimic these regulators, demonstrating their translational importance. Another facet of LPL biology is that the oligomeric state of the enzyme is also central to its regulation. Recent structural studies have solidified the idea that LPL is regulated not only by interactions with other binding partners but also by self-associations. Here, we review the complexities of the protein-protein and protein-lipid interactions that govern LPL structure and function.

The GPIHBP1-LPL complex and its role in plasma triglyceride metabolism: Insights into chylomicronemia

GPIHBP1 is a protein found in the endothelial cells of capillaries that is anchored by glycosylphosphatidylinositol and binds to high-density lipoproteins. GPIHBP1 attaches to lipoprotein lipase (LPL), subsequently carrying the enzyme and anchoring it to the capillary lumen. Enabling lipid metabolism is essential for the marginalization of lipoproteins alongside capillaries. Studies underscore the significance of GPIHBP1 in transporting, stabilizing, and aiding in the marginalization of LPL. The intricate interplay between GPIHBP1 and LPL has provided novel insights into chylomicronemia in recent years. Mutations hindering the formation or reducing the efficiency of the GPIHBP1-LPL complex are central to the onset of chylomicronemia. This review delves into the structural nuances of the GPIHBP1-LPL interaction, the consequences of mutations in the complex leading to chylomicronemia, and cutting-edge advancements in chylomicronemia treatment.

Short hydrocarbon stapled ApoC2-mimetic peptides activate lipoprotein lipase and lower plasma triglycerides in mice

Introduction

Defects in lipolysis can lead to hypertriglyceridemia, which can trigger acute pancreatitis and is also associated with cardiovascular disease. Decreasing plasma triglycerides (TGs) by activating lipoprotein lipase (LPL) with ApoC2 mimetic peptides is a new treatment strategy for hypertriglyceridemia. We recently described a dual ApoC2 mimetic/ApoC3 antagonist peptide called D6PV that effectively lowered TG in several mouse models but has limitations in terms of drug development. The aim of this study was to create the next generation of ApoC2 mimetic peptides.

Methods

We employed hydrocarbon staples, as well as select amino acid substitutions, to make short single helical mimetic peptides based on the last helix of ApoC2. Peptides were first tested for their ability to activate LPL and then in hypertriglyceridemia mouse models. All-atom simulations of peptides were performed in a lipid-trilayer model of TG-rich lipoproteins to discern their possible mechanism of action.

Results

We designed a single stapled peptide called SP1 (21 residues), and a double stapled (stitched) peptide called SP2 (21 residues) and its N-terminal acylated analogue, SP2a. The hydrocarbon staples increased the amphipathicity of the peptides and their ability to bind lipids without interfering with LPL activation. Indeed, from all-atom simulations, the conformations of SP1 and SP2a are restrained by the staples and maintains the proper orientation of the LPL activation motif, while still allowing their deeper insertion into the lipid-trilayer model. Intraperitoneal injection of stapled peptides (1-5 umoles/kg) into ApoC2-hypomorphic mice or human ApoC3-transgenic resulted in an 80%-90% reduction in plasma TG within 3 h, similar to the much longer D6PV peptide (41 residues). Other modifications (replacement L-Glu20, L-Glu21 with their D-isomers, N-methylation of Gly19, Met2NorLeu and Ala1alpha-methylAla substitutions, N-terminal octanoylation) were introduced into the SP2a peptide. These changes made SP2a highly resistant to proteolysis against trypsin, pepsin, and Proteinase K, while maintaining similar efficacy in lowering plasma TG in mice.

Conclusion

We describe a new generation of ApoC2 mimetic peptides based on hydron carbon stapling that are at least equally potent to earlier peptides but are much shorter and resistant to proteolysis and could be further developed into a new therapy for hypertriglyceridemia.

Quartet of APOCs and the Different Roles They Play in Diabetes

APOA1 and APOB are the structural proteins of high-density lipoprotein and APOB-containing lipoproteins, such as low-density lipoprotein and very low-density lipoprotein, respectively. The 4 smaller APOCs (APOC1, APOC2, APOC3, and APOC4) are exchangeable apolipoproteins; they are readily transferred among high-density lipoproteins and APOB-containing lipoproteins. The APOCs regulate plasma triglyceride and cholesterol levels by modulating substrate availability and activities of enzymes interacting with lipoproteins and by interfering with APOB-containing lipoprotein uptake through hepatic receptors. Of the 4 APOCs, APOC3 has been best studied in relation to diabetes. Elevated serum APOC3 levels predict incident cardiovascular disease and progression of kidney disease in people with type 1 diabetes. Insulin suppresses APOC3 levels, and accordingly, elevated APOC3 levels associate with insulin deficiency and insulin resistance. Mechanistic studies in a mouse model of type 1 diabetes have demonstrated that APOC3 acts in the causal pathway of diabetes-accelerated atherosclerosis. The mechanism is likely due to the ability of APOC3 to slow the clearance of triglyceride-rich lipoproteins and their remnants, thereby causing an increased accumulation of atherogenic lipoprotein remnants in lesions of atherosclerosis. Less is known about the roles of APOC1, APOC2, and APOC4 in diabetes.

A Current Update on the Role of HDL-Based Nanomedicine in Targeting Macrophages in Cardiovascular Disease

High-density lipoproteins (HDL) are complex endogenous nanoparticles involved in important functions such as reverse cholesterol transport and immunomodulatory activities, ensuring metabolic homeostasis and vascular health. The ability of HDL to interact with a plethora of immune cells and structural cells places it in the center of numerous disease pathophysiologies. However, inflammatory dysregulation can lead to pathogenic remodeling and post-translational modification of HDL, rendering HDL dysfunctional or even pro-inflammatory. Monocytes and macrophages play a critical role in mediating vascular inflammation, such as in coronary artery disease (CAD). The fact that HDL nanoparticles have potent anti-inflammatory effects on mononuclear phagocytes has opened new avenues for the development of nanotherapeutics to restore vascular integrity. HDL infusion therapies are being developed to improve the physiological functions of HDL and to quantitatively restore or increase the native HDL pool. The components and design of HDL-based nanoparticles have evolved significantly since their initial introduction with highly anticipated results in an ongoing phase III clinical trial in subjects with acute coronary syndrome. The understanding of mechanisms involved in HDL-based synthetic nanotherapeutics is critical to their design, therapeutic potential and effectiveness. In this review, we provide a current update on HDL-ApoA-I mimetic nanotherapeutics, highlighting the scope of treating vascular diseases by targeting monocytes and macrophages.

Inverse association between apolipoprotein C-II and cardiovascular mortality: role of lipoprotein lipase activity modulation

AIMS

Apolipoprotein C-II (ApoC-II) is thought to activate lipoprotein lipase (LPL) and is therefore a possible target for treating hypertriglyceridemia. Its relationship with cardiovascular risk has not been investigated in large-scale epidemiologic studies, particularly allowing for apolipoprotein C-III (ApoC-III), an LPL antagonist. Furthermore, the exact mechanism of ApoC-II-mediated LPL activation is unclear.

METHODS AND RESULTS

ApoC-II was measured in 3141 LURIC participants of which 590 died from cardiovascular diseases during a median (inter-quartile range) follow-up of 9.9 (8.7-10.7) years. Apolipoprotein C-II-mediated activation of the glycosylphosphatidylinositol high-density lipoprotein binding protein 1 (GPIHBP1)-LPL complex was studied using enzymatic activity assays with fluorometric lipase and very low-density lipoprotein (VLDL) substrates. The mean ApoC-II concentration was 4.5 (2.4) mg/dL. The relationship of ApoC-II quintiles with cardiovascular mortality exhibited a trend toward an inverse J-shape, with the highest risk in the first (lowest) quintile and lowest risk in the middle quintile. Compared with the first quintile, all other quintiles were associated with decreased cardiovascular mortality after multivariate adjustments including ApoC-III as a covariate (all P < 0.05). In experiments using fluorometric substrate-based lipase assays, there was a bell-shaped relationship for the effect of ApoC-II on GPIHBP1-LPL activity when exogenous ApoC-II was added. In ApoC-II-containing VLDL substrate-based lipase assays, GPIHBP1-LPL enzymatic activity was almost completely blocked by a neutralizing anti-ApoC-II antibody.

CONCLUSION

The present epidemiologic data suggest that increasing low circulating ApoC-II levels may reduce cardiovascular risk. This conclusion is supported by the observation that optimal ApoC-II concentrations are required for maximal GPIHBP1-LPL enzymatic activity.

Inverse effects of APOC2 and ANGPTL4 on the conformational dynamics of lid-anchoring structures in lipoprotein lipase

The lipolytic processing of triglyceride-rich lipoproteins (TRLs) by lipoprotein lipase (LPL) is crucial for the delivery of dietary lipids to the heart, skeletal muscle, and adipose tissue. The processing of TRLs by LPL is regulated in a tissue-specific manner by a complex interplay between activators and inhibitors. Angiopoietin-like protein 4 (ANGPTL4) inhibits LPL by reducing its thermal stability and catalyzing the irreversible unfolding of LPL's α/β-hydrolase domain. We previously mapped the ANGPTL4 binding site on LPL and defined the downstream unfolding events resulting in LPL inactivation. The binding of LPL to glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 protects against LPL unfolding. The binding site on LPL for an activating cofactor, apolipoprotein C2 (APOC2), and the mechanisms by which APOC2 activates LPL have been unclear and controversial. Using hydrogen-deuterium exchange/mass spectrometry, we now show that APOC2's C-terminal α-helix binds to regions of LPL surrounding the catalytic pocket. Remarkably, APOC2's binding site on LPL overlaps with that for ANGPTL4, but their effects on LPL conformation are distinct. In contrast to ANGPTL4, APOC2 increases the thermal stability of LPL and protects it from unfolding. Also, the regions of LPL that anchor the lid are stabilized by APOC2 but destabilized by ANGPTL4, providing a plausible explanation for why APOC2 is an activator of LPL, while ANGPTL4 is an inhibitor. Our studies provide fresh insights into the molecular mechanisms by which APOC2 binds and stabilizes LPL-and properties that we suspect are relevant to the conformational gating of LPL's active site.

Broadening the Scope of Dyslipidemia Therapy by Targeting APOC3 (Apolipoprotein C3) and ANGPTL3 (Angiopoietin-Like Protein 3)

The positive relationship between increased levels of circulating triglycerides and cardiovascular events has been observed for decades. Driven by genetic cohort studies, inhibitors of APOC3 (apolipoprotein C3) and ANGPTL (angiopoietin-like protein) 3 that reduce circulating triglycerides are poised to enter clinical practice. We will review the biology of how inhibition of these 2 proteins affects circulating lipoproteins as well as the current state of clinical development of monoclonal antibodies, antisense oligonucleotides, and silencing RNAs targeting APOC3 and ANGPTL3.

Increased Weight Gain and Insulin Resistance in HF-Fed PLTP Deficient Mice Is Related to Altered Inflammatory Response and Plasma Transport of Gut-Derived LPS

Bacterial lipopolysaccharides (LPS, endotoxins) are found in high amounts in the gut lumen. LPS can cross the gut barrier and pass into the blood (endotoxemia), leading to low-grade inflammation, a common scheme in metabolic diseases. Phospholipid transfer protein (PLTP) can transfer circulating LPS to plasma lipoproteins, thereby promoting its detoxification. However, the impact of PLTP on the metabolic fate and biological effects of gut-derived LPS is unknown. This study aimed to investigate the influence of PLTP on low-grade inflammation, obesity and insulin resistance in relationship with LPS intestinal translocation and metabolic endotoxemia. Wild-type (WT) mice were compared with Pltp-deficient mice (Pltp-KO) after a 4-month high-fat (HF) diet or oral administration of labeled LPS. On a HF diet, Pltp-KO mice showed increased weight gain, adiposity, insulin resistance, lipid abnormalities and inflammation, together with a higher exposure to endotoxemia compared to WT mice. After oral administration of LPS, PLTP deficiency led to increased intestinal translocation and decreased association of LPS to lipoproteins, together with an altered catabolism of triglyceride-rich lipoproteins (TRL). Our results show that PLTP, by modulating the intestinal translocation of LPS and plasma processing of TRL-bound LPS, has a major impact on low-grade inflammation and the onset of diet-induced metabolic disorders.

Alterations of HDL's to piHDL's Proteome in Patients with Chronic Inflammatory Diseases, and HDL-Targeted Therapies

Chronic inflammatory diseases, such as rheumatoid arthritis, steatohepatitis, periodontitis, chronic kidney disease, and others are associated with an increased risk of atherosclerotic cardiovascular disease, which persists even after accounting for traditional cardiac risk factors. The common factor linking these diseases to accelerated atherosclerosis is chronic systemic low-grade inflammation triggering changes in lipoprotein structure and metabolism. HDL, an independent marker of cardiovascular risk, is a lipoprotein particle with numerous important anti-atherogenic properties. Besides the essential role in reverse cholesterol transport, HDL possesses antioxidative, anti-inflammatory, antiapoptotic, and antithrombotic properties. Inflammation and inflammation-associated pathologies can cause modifications in HDL's proteome and lipidome, transforming HDL from atheroprotective into a pro-atherosclerotic lipoprotein. Therefore, a simple increase in HDL concentration in patients with inflammatory diseases has not led to the desired anti-atherogenic outcome. In this review, the functions of individual protein components of HDL, rendering them either anti-inflammatory or pro-inflammatory are described in detail. Alterations of HDL proteome (such as replacing atheroprotective proteins by pro-inflammatory proteins, or posttranslational modifications) in patients with chronic inflammatory diseases and their impact on cardiovascular health are discussed. Finally, molecular, and clinical aspects of HDL-targeted therapies, including those used in therapeutical practice, drugs in clinical trials, and experimental drugs are comprehensively summarised.

The Regulation of Triacylglycerol Metabolism and Lipoprotein Lipase Activity

Triacylglycerol (TG) metabolism is tightly regulated to maintain a pool of TG within circulating lipoproteins that can be hydrolyzed in a tissue-specific manner by lipoprotein lipase (LPL) to enable the delivery of fatty acids to adipose or oxidative tissues as needed. Elevated serum TG concentrations, which result from a deficiency of LPL activity or, more commonly, an imbalance in the regulation of tissue-specific LPL activities, have been associated with an increased risk of atherosclerotic cardiovascular disease through multiple studies. Among the most critical LPL regulators are the angiopoietin-like (ANGPTL) proteins ANGPTL3, ANGPTL4, and ANGPTL8, and a number of different apolipoproteins including apolipoprotein A5 (ApoA5), apolipoprotein C2 (ApoC2), and apolipoprotein C3 (ApoC3). These ANGPTLs and apolipoproteins work together to orchestrate LPL activity and therefore play pivotal roles in TG partitioning, hydrolysis, and utilization. This review summarizes the mechanisms of action, epidemiological findings, and genetic data most relevant to these ANGPTLs and apolipoproteins. The interplay between these important regulators of TG metabolism in both fasted and fed states is highlighted with a holistic view toward understanding key concepts and interactions. Strategies for developing safe and effective therapeutics to reduce circulating TG by selectively targeting these ANGPTLs and apolipoproteins are also discussed.

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.

Triglyceride and Triglyceride-Rich Lipoproteins in Atherosclerosis

Cardiovascular disease (CVD) is still the leading cause of death globally, and atherosclerosis is the main pathological basis of CVDs. Low-density lipoprotein cholesterol (LDL-C) is a strong causal factor of atherosclerosis. However, the first-line lipid-lowering drugs, statins, only reduce approximately 30% of the CVD risk. Of note, atherosclerotic CVD (ASCVD) cannot be eliminated in a great number of patients even their LDL-C levels meet the recommended clinical goals. Previously, whether the elevated plasma level of triglyceride is causally associated with ASCVD has been controversial. Recent genetic and epidemiological studies have demonstrated that triglyceride and triglyceride-rich lipoprotein (TGRL) are the main causal risk factors of the residual ASCVD. TGRLs and their metabolites can promote atherosclerosis via modulating inflammation, oxidative stress, and formation of foam cells. In this article, we will make a short review of TG and TGRL metabolism, display evidence of association between TG and ASCVD, summarize the atherogenic factors of TGRLs and their metabolites, and discuss the current findings and advances in TG-lowering therapies. This review provides information useful for the researchers in the field of CVD as well as for pharmacologists and clinicians.

Molecular Condensate in a Membrane: A Tugging Game between Hydrophobicity and Polarity with Its Biological Significance

Lipid self-organization and lipid-water interfaces have been an increasingly important topic positioned at the crossroads of physical chemistry and biology. Some neutral lipids can partition into the biomembrane and play an important biological role. In this study, we have used all-atom molecular dynamics simulations to dissect the partition, aggregation, flip-flop, and modulation of neutral lipids including (i) menaquinone/menaquinol, (ii) ubiquinone/ubiquinol, and (iii) triacylglycerol. The partitioning of these molecules is driven by the balancing force between headgroup hydrophilicity and acyl chain hydrophobicity as well as the lipid shapes. We then discuss the emerging questions in this area, share our own perspectives, and mention the development of the CHARMM-GUI membrane modeling platform, which enables further computational investigations into those questions.

New therapeutic approaches for the treatment of hypertriglyceridemia

Patients with hypertriglyceridemia (> 150 mg/dl) have an increased risk for atherosclerotic cardiovascular disease, and those with severe hypertriglyceridemia (> 880 mg/dl) also for pancreatitis. The currently available medications to decrease triglyceride levels, such as fibrates, statins, and omega‑3 fatty acids, are in many cases not able to achieve normal triglyceride levels. Therefore, new drugs are in development to address this unmet need. Recently, icosapent ethyl, a purified formulation of the omega-3-fatty acid eicosapentaenoic acid, was approved in Germany for the reduction of cardiovascular events in patients with hypertriglyceridemia and established cardiovascular disease or with diabetes and other risk factors on top of statins. Other new drugs in development are the more selective peroxisome proliferator-activated receptor α (PPARα) modulator, pemafibrate, already approved for the treatment of hypertriglyceridemia in Japan, and inhibitors of ApoC-III and angiopoietin-like 3 (ANGPTL3) in the form of antisense oligonucleotides or siRNAs or fully human monoclonal binding antibodies. Apolipoprotein C-III and ANGPTL3 protein seem to be quite promising targets based on solid genetic data. Larger studies of long duration, many of them currently ongoing, are needed to establish the role these medications will play in the treatment of hypertriglyceridemia in clinical practice.

Complex association of apolipoprotein E-containing HDL with coronary artery disease burden in cardiovascular disease

Background

Although traditional lipid parameters and coronary imaging techniques are valuable for cardiovascular disease (CVD) risk prediction, better diagnostic tests are still needed.

Methods

In a prospective, observational study, 795 individuals had extensive cardiometabolic profiling, including emerging biomarkers, such as apolipoprotein E–containing HDL-cholesterol (ApoE-HDL-C). Coronary artery calcium (CAC) score was assessed in the entire cohort, and quantitative coronary computed tomography angiography (CCTA) characterization of total burden, noncalcified burden (NCB), and fibrous plaque burden (FB) was performed in a subcohort (n = 300) of patients stratified by concentration of ApoE-HDL-C. Total and HDL-containing apolipoprotein C-III (ApoC-III) were also measured.

Results

Most patients had a clinical diagnosis of coronary artery disease (CAD) (n = 80.4% of 795), with mean age of 59 years, a majority being male (57%), and about half on statin treatment. The low ApoE-HDL-C group had more severe stenosis (11% vs. 2%, overall P < 0.001), with higher CAC as compared with high ApoE-HDL-C. On quantitative CCTA, the high ApoE-HDL-C group had lower NCB (β = –0.24, P = 0.0001), which tended to be significant in a fully adjusted model (β = –0.32, P = 0.001) and altered by ApoC-III in HDL levels. Low ApoE-HDL-C was significantly associated with LDL particle number (β = 0.31; P = 0.0001). Finally, when stratified by FB, ApoC-III in HDL showed a more robust predictive value of CAD over ApoE-HDL-C (AUC: 0.705, P = 0.0001) in a fully adjusted model.

Conclusion

ApoE-containing HDL-C showed a significant association with early coronary plaque characteristics and is affected by the presence of ApoC-III, indicating that low ApoE-HDL-C and high ApoC-III may be important markers of CVD severity.

Trial Registration

ClinicalTrials.gov: NCT01621594.

Funding

This work was supported by the NHLBI at the NIH Intramural Research Program.

Computational Studies of Lipid Droplets

Lipid droplets (LDs) are intracellular organelles whose primary function is energy storage. Known to emerge from the endoplasmic reticulum (ER) bilayer, LDs have a unique structure with a core consisting of neutral lipids, triacylglycerol (TG) or sterol esters (SE), surrounded by a phospholipid (PL) monolayer and decorated by proteins that come and go throughout their complex lifecycle. In this Feature Article, we review recent developments in computational studies of LDs, a rapidly growing area of research. We highlight how molecular dynamics (MD) simulations have provided valuable molecular-level insight into LD targeting and LD biogenesis. Additionally, we review the physical properties of TG from different force fields compared with experimental data. Possible future directions and challenges are discussed.

Metabolism of triglyceride-rich lipoproteins in health and dyslipidaemia

Accumulating evidence points to the causal role of triglyceride-rich lipoproteins and their cholesterol-enriched remnants in atherogenesis. Genetic studies in particular have not only revealed a relationship between plasma triglyceride levels and the risk of atherosclerotic cardiovascular disease, but have also identified key proteins responsible for the regulation of triglyceride transport. Kinetic studies in humans using stable isotope tracers have been especially useful in delineating the function of these proteins and revealing the hitherto unappreciated complexity of triglyceride-rich lipoprotein metabolism. Given that triglyceride is an essential energy source for mammals, triglyceride transport is regulated by numerous mechanisms that balance availability with the energy demands of the body. Ongoing investigations are focused on determining the consequences of dysregulation as a result of either dietary imprudence or genetic variation that increases the risk of atherosclerosis and pancreatitis. The identification of molecular control mechanisms involved in triglyceride metabolism has laid the groundwork for a 'precision-medicine' approach to therapy. Novel pharmacological agents under development have specific molecular targets within a regulatory framework, and their deployment heralds a new era in lipid-lowering-mediated prevention of disease. In this Review, we outline what is known about the dysregulation of triglyceride transport in human hypertriglyceridaemia.

Apolipoproteins in vascular biology and atherosclerotic disease

Apolipoproteins are important structural components of plasma lipoproteins that influence vascular biology and atherosclerotic disease pathophysiology by regulating lipoprotein metabolism. Clinically important apolipoproteins related to lipid metabolism and atherogenesis include apolipoprotein B-100, apolipoprotein B-48, apolipoprotein A-I, apolipoprotein C-II, apolipoprotein C-III, apolipoprotein E and apolipoprotein(a). Apolipoprotein B-100 is the major structural component of VLDL, IDL, LDL and lipoprotein(a). Apolipoprotein B-48 is a truncated isoform of apolipoprotein B-100 that forms the backbone of chylomicrons. Apolipoprotein A-I provides the scaffolding for lipidation of HDL and has an important role in reverse cholesterol transport. Apolipoproteins C-II, apolipoprotein C-III and apolipoprotein E are involved in triglyceride-rich lipoprotein metabolism. Apolipoprotein(a) covalently binds to apolipoprotein B-100 to form lipoprotein(a). In this Review, we discuss the mechanisms by which these apolipoproteins regulate lipoprotein metabolism and thereby influence vascular biology and atherosclerotic disease. Advances in the understanding of apolipoprotein biology and their translation into therapeutic agents to reduce the risk of cardiovascular disease are also highlighted.

Addressing dyslipidemic risk beyond LDL-cholesterol

Despite the success of LDL-lowering drugs in reducing cardiovascular disease (CVD), there remains a large burden of residual disease due in part to persistent dyslipidemia characterized by elevated levels of triglyceride-rich lipoproteins (TRLs) and reduced levels of HDL. This form of dyslipidemia is increasing globally as a result of the rising prevalence of obesity and metabolic syndrome. Accumulating evidence suggests that impaired hepatic clearance of cholesterol-rich TRL remnants leads to their accumulation in arteries, promoting foam cell formation and inflammation. Low levels of HDL may associate with reduced cholesterol efflux from foam cells, aggravating atherosclerosis. While fibrates and fish oils reduce TRL, they have not been uniformly successful in reducing CVD, and there is a large unmet need for new approaches to reduce remnants and CVD. Rare genetic variants that lower triglyceride levels via activation of lipolysis and associate with reduced CVD suggest new approaches to treating dyslipidemia. Apolipoprotein C3 (APOC3) and angiopoietin-like 3 (ANGPTL3) have emerged as targets for inhibition by antibody, antisense, or RNAi approaches. Inhibition of either molecule lowers TRL but respectively raises or lowers HDL levels. Large clinical trials of such agents in patients with high CVD risk and elevated levels of TRL will be required to demonstrate efficacy of these approaches.

Guanidinylated Apolipoprotein C3 (ApoC3) Associates with Kidney and Vascular Injury

BACKGROUND

Coexistent CKD and cardiovascular diseases are highly prevalent in Western populations and account for substantial mortality. We recently found that apolipoprotein C-3 (ApoC3), a major constituent of triglyceride-rich lipoproteins, induces sterile systemic inflammation by activating the NOD-like receptor protein-3 (NLRP3) inflammasome in human monocytes via an alternative pathway.

METHODS

To identify posttranslational modifications of ApoC3 in patients with CKD, we used mass spectrometry to analyze ApoC3 from such patients and from healthy individuals. We determined the effects of posttranslationally modified ApoC3 on monocyte inflammatory response in vitro, as well as in humanized mice subjected to unilateral ureter ligation (a kidney fibrosis model) and in a humanized mouse model for vascular injury and regeneration. Finally, we conducted a prospective observational trial of 543 patients with CKD to explore the association of posttranslationally modified ApoC3 with renal and cardiovascular events in such patients.

RESULTS

We identified significant posttranslational guanidinylation of ApoC3 (gApoC3) in patients with CKD. We also found that mechanistically, guanidine and urea induce guanidinylation of ApoC3. A 2D-proteomic analysis revealed that gApoC3 accumulated in kidneys and plasma in a CKD mouse model (mice fed an adenine-rich diet). In addition, gApoC3 augmented the proinflammatory effects of ApoC3 in monocytes in vitro . In humanized mice, gApoC3 promoted kidney tissue fibrosis and impeded vascular regeneration. In CKD patients, higher gApoC3 plasma levels (as determined by mass spectrometry) were associated with increased mortality as well as with renal and cardiovascular events.

CONCLUSIONS

Guanidinylation of ApoC3 represents a novel pathogenic mechanism in CKD and CKD-associated vascular injury, pointing to gApoC3 as a potential therapeutic target.

Apolipoprotein and LRP1-Based Peptides as New Therapeutic Tools in Atherosclerosis

Apolipoprotein (Apo)-based mimetic peptides have been shown to reduce atherosclerosis. Most of the ApoC-II and ApoE mimetics exert anti-atherosclerotic effects by improving lipid profile. ApoC-II mimetics reverse hypertriglyceridemia and ApoE-based peptides such as Ac-hE18A-NH2 reduce cholesterol and triglyceride (TG) levels in humans. Conversely, other classes of ApoE and ApoA-I mimetic peptides and, more recently, ApoJ and LRP1-based peptides, exhibit several anti-atherosclerotic actions in experimental models without influencing lipoprotein profile. These other mimetic peptides display at least one atheroprotective mechanism such as providing LDL stability against mechanical modification or conferring protection against the action of lipolytic enzymes inducing LDL aggregation in the arterial intima. Other anti-atherosclerotic effects exerted by these peptides also include protection against foam cell formation and inflammation, and induction of reverse cholesterol transport. Although the underlying mechanisms of action are still poorly described, the recent findings suggest that these mimetics could confer atheroprotection by favorably influencing lipoprotein function rather than lipoprotein levels. Despite the promising results obtained with peptide mimetics, the assessment of their stability, atheroprotective efficacy and tissue targeted delivery are issues currently under progress.

Apolipoprotein C-II induces EMT to promote gastric cancer peritoneal metastasis via PI3K/AKT/mTOR pathway

BACKGROUND

Peritoneal metastasis (PM) occurs frequently in patients with gastric cancer (GC) and confers poor survival. Lipid metabolism acts as a non-negligible regulator in epithelial-mesenchymal transition (EMT), which is crucial for the metastasis of GC. As apolipoprotein C2 (APOC2) is a key activator of lipoprotein lipase for triglyceride metabolism, the exact mechanism of APOC2 remains largely unknown in GC.

METHODS

Tandem mass tags identified differentially expressed proteins between human PM and GC tissues, and showed that APOC2 overexpressed in PM tissues, which was further confirmed by immunoblotting, immunohistochemistry, and ELISA. Global gene expression changes were identified in APOC2 knockdown cells via RNA-sequencing. The role of APOC2 in lipid metabolism of GC cells was assessed via the Seahorse XF analyzer and lipid staining assays. The biological role of APOC2 in GC cells was determined by 3D Spheroid invasion, apoptosis, colony formation, wound healing, transwell assay, and mouse models. The interaction between APOC2 and CD36 was analyzed by co-immunoprecipitation and biolayer interferometry. The underlying mechanisms were investigated using western blot technique.

RESULTS

APOC2 overexpressed in GC PM tissues. Upregulation of APOC2 correlated with a poor prognosis in GC patients. APOC2 promoted GC cell invasion, migration, and proliferation via CD36-mediated PI3K/AKT/mTOR signaling activation. Furthermore, APOC2-CD36 axis upregulated EMT markers of GC cells via increasing the phosphorylation of PI3K, AKT, and mTOR. Knockdown either APOC2 or CD36 inhibited the malignant phenotype of cancer cells, and delayed GC PM progression in murine GC models.

CONCLUSION

APOC2 cooperates with CD36 to induce EMT to promote GC PM via PI3K/AKT/mTOR pathway. APOC2-CD36 axis may be a potential target for the treatment of aggressive GC.

The Importance of Lipoprotein Lipase Regulation in Atherosclerosis

Lipoprotein lipase (LPL) plays a major role in the lipid homeostasis mainly by mediating the intravascular lipolysis of triglyceride rich lipoproteins. Impaired LPL activity leads to the accumulation of chylomicrons and very low-density lipoproteins (VLDL) in plasma, resulting in hypertriglyceridemia. While low-density lipoprotein cholesterol (LDL-C) is recognized as a primary risk factor for atherosclerosis, hypertriglyceridemia has been shown to be an independent risk factor for cardiovascular disease (CVD) and a residual risk factor in atherosclerosis development. In this review, we focus on the lipolysis machinery and discuss the potential role of triglycerides, remnant particles, and lipolysis mediators in the onset and progression of atherosclerotic cardiovascular disease (ASCVD). This review details a number of important factors involved in the maturation and transportation of LPL to the capillaries, where the triglycerides are hydrolyzed, generating remnant lipoproteins. Moreover, LPL and other factors involved in intravascular lipolysis are also reported to impact the clearance of remnant lipoproteins from plasma and promote lipoprotein retention in capillaries. Apolipoproteins (Apo) and angiopoietin-like proteins (ANGPTLs) play a crucial role in regulating LPL activity and recent insights into LPL regulation may elucidate new pharmacological means to address the challenge of hypertriglyceridemia in atherosclerosis development.

Lipolytic enzymes and free fatty acids at the endothelial interface

Lipids released from circulating lipoproteins by intravascular action of lipoprotein lipase (LpL) reach parenchymal cells in tissues with a non-fenestrated endothelium by transfer through or around endothelial cells. The actions of LpL are controlled at multiple sites, its synthesis and release by myocytes and adipocytes, its transit and association with the endothelial cell luminal surface, and finally its activation and inhibition by a number of proteins and by its product non-esterified fatty acids. Multiple pathways mediate endothelial transit of lipids into muscle and adipose tissues. These include movement of fatty acids via the endothelial cell fatty acid transporter CD36 and movement of whole or partially LpL-hydrolyzed lipoproteins via other apical endothelial cell receptors such as SR-B1and Alk1. Lipids also likely change the barrier function of the endothelium and operation of the paracellular pathway around endothelial cells. This review summarizes in vitro and in vivo support for the key role of endothelial cells in delivery of lipids and highlights incompletely understood processes that are the focus of active investigation.

Treatment of mild-to-moderate hypertriglyceridemia

The atherogenic role of triglycerides (TG) as an independent cardiovascular risk factor has been discussed for many years, largely because hypertriglyceridaemia (HTG) is a complex metabolic entity of multiple aetiology involving processes of diverse nature. In this chapter, a discussion will be presented on the current recommendations for the management of mild-moderate hypertriglyceridaemia (150-880mg/dL). The aim of the interventions used is to decrease the LDL-cholesterol (c-LDL) and control the HTG. This entails reducing apoprotein B (ApoB) levels, the number of remaining TG-rich lipoproteins (LRP), non-HDL-cholesterol (c-non-HDL), and increasing HDL-cholesterol (c-HDL). The management strategy includes healthy lifestyle recommendations, and subsequent use of lipid-lowering drugs, including statins, fibrates, n-3 fatty acids and PCSK9 inhibitors.

Apolipoprotein Mimetic Peptides: Potential New Therapies for Cardiovascular Diseases

Since the seminal breakthrough of treating diabetic patients with insulin in the 1920s, there has been great interest in developing other proteins and their peptide mimetics as therapies for a wide variety of other medical disorders. Currently, there are at least 60 different peptides that have been approved for human use and over 150 peptides that are in various stages of clinical development. Peptides mimetic of the major proteins on lipoproteins, namely apolipoproteins, have also been developed first as tools for understanding apolipoprotein structure and more recently as potential therapeutics. In this review, we discuss the biochemistry, peptide mimetics design and clinical trials for peptides based on apoA-I, apoE and apoC-II. We primarily focus on applications of peptide mimetics related to cardiovascular diseases. We conclude with a discussion on the limitations of peptides as therapeutic agents and the challenges that need to be overcome before apolipoprotein mimetic peptides can be developed into new drugs.

Apolipoprotein CIII and Angiopoietin-like Protein 8 are Elevated in Lipodystrophy and Decrease after Metreleptin

Context

Lipodystrophy syndromes cause hypertriglyceridemia that improves with leptin treatment using metreleptin. Mechanisms causing hypertriglyceridemia and improvements after metreleptin are incompletely understood.

Objective

Determine relationship of circulating lipoprotein lipase (LPL) modulators with hypertriglyceridemia in healthy controls and in patients with lipodystrophy before and after metreleptin.

Methods

Cross-sectional comparison of patients with lipodystrophy (generalized lipodystrophy n = 3; partial lipodystrophy n = 11) vs age/sex-matched healthy controls (n = 28), and longitudinal analyses in patients before and after 2 weeks and 6 months of metreleptin. The study was carried out at the National Institutes of Health, Bethesda, Maryland. Outcomes were LPL stimulators apolipoprotein (apo) C-II and apoA-V and inhibitors apoC-III and angiopoietin-like proteins (ANGPTLs) 3, 4, and 8; ex vivo activation of LPL by plasma.

Results

Patients with lipodystrophy were hypertriglyceridemic and had higher levels of all LPL stimulators and inhibitors vs controls except for ANGPTL4, with >300-fold higher ANGPTL8, 4-fold higher apoC-III, 3.5-fold higher apoC-II, 1.9-fold higher apoA-V, 1.6-fold higher ANGPTL3 (P < .05 for all). At baseline, all LPL modulators except ANGPLT4 positively correlated with triglycerides. Metreleptin decreased apoC-II and apoC-III after 2 weeks and 6 months, and decreased ANGPTL8 after 6 months (P < 0.05 for all). Plasma from patients with lipodystrophy caused higher ex vivo LPL activation vs hypertriglyceridemic control plasma (P < .0001), which did not change after metreleptin.

Conclusion

Elevations in LPL inhibitors apoC-III and ANGPTL8 may contribute to hypertriglyceridemia in lipodystrophy, and may mediate reductions in circulating and hepatic triglycerides after metreleptin. These therefore are strong candidates for therapies to lower triglycerides in these patients.

Hypertriglyceridemia: new approaches in management and treatment

PURPOSE OF REVIEW

Hypertriglyceridemia (HTG), a form of dyslipidemia characterized by elevated plasma of triglycerides (TG), is associated with an increased risk for acute pancreatitis. Moreover, HTG has recently been shown to be linked to the development of atherosclerotic cardiovascular disease (ASCVD); therefore, there is a great interest in better understanding the pathophysiology of HTG and improving its clinical management. In this review, we briefly describe TG metabolism, recent guidelines for the clinical management of HTG and provide an overview of the current and potential new therapies for HTG.

RECENT FINDINGS

Screening patients for HTG is valuable for not only identifying patients with extreme TG elevations, who are at risk for pancreatitis, but also for managing ASCVD risk in patients with more moderate forms of HTG. Therefore, the most recent USA guidelines for cardiovascular diseases recommend using TG as a risk enhancer test, leading to a more aggressive treatment of patients with intermediate risk. Currently, there are several available approaches for reducing plasma TG, which include lifestyle changes, fibrates and omega-3 fatty acid treatment. The addition of eicosapentaenoic acid (EPA) on top of statins has recently been shown to significantly reduce ASCVD events. Nevertheless, there is an unmet need for more effective treatment options. Several new therapies based on newly identified targets in TG metabolism, such as apolipoprotein C-III and angiopoietin-like 3 protein, are currently under development.

SUMMARY

The clinical management of HTG is important in the prevention and treatment of acute pancreatitis and also impacts on how ASCVD risk is managed. More work needs to be done to establish the mechanism for the ability of how EPA lowers ASCVD and how to best integrate it with other lipid-lowering therapies. The efficacy and safety of the novel therapies for HTG should be established soon in the ongoing late-stage clinical trials.

The Role of HDL and HDL Mimetic Peptides as Potential Therapeutics for Alzheimer's Disease

The role of high-density lipoproteins (HDL) in the cardiovascular system has been extensively studied and the cardioprotective effects of HDL are well established. As HDL particles are formed both in the systemic circulation and in the central nervous system, the role of HDL and its associated apolipoproteins in the brain has attracted much research interest in recent years. Alzheimer’s disease (AD) is the most prevalent neurodegenerative disorder and the leading cause of dementia worldwide, for which there currently exists no approved disease modifying treatment. Multiple lines of evidence, including a number of large-scale human clinical studies, have shown a robust connection between HDL levels and AD. Low levels of HDL are associated with increased risk and severity of AD, whereas high levels of HDL are correlated with superior cognitive function. Although the mechanisms underlying the protective effects of HDL in the brain are not fully understood, many of the functions of HDL, including reverse lipid/cholesterol transport, anti-inflammation/immune modulation, anti-oxidation, microvessel endothelial protection, and proteopathy modification, are thought to be critical for its beneficial effects. This review describes the current evidence for the role of HDL in AD and the potential of using small peptides mimicking HDL or its associated apolipoproteins (HDL-mimetic peptides) as therapeutics to treat AD.

Volanesorsen in the Treatment of Familial Chylomicronemia Syndrome or Hypertriglyceridaemia: Design, Development and Place in Therapy

Severe hypertriglyceridaemia is associated with pancreatitis and chronic pancreatitis-induced diabetes. Familial chylomicronaemia syndrome (FCS) is a rare autosomal recessive disorder of lipid metabolism characterised by high levels of triglycerides (TGs) due to failure of chylomicron clearance. It causes repeated episodes of severe abdominal pain, fatigue and attacks of acute pancreatitis. There are few current options for its long-term management. The only universal long-term therapy is restriction of total dietary fat intake to <10-15% of daily calories (15 to 20g per day). Many patients have been treated with fibrates and statins with a variable response, but many remain susceptible to pancreatitis. Other genetic syndromes associated with hypertriglyceridaemia include familial partial lipodystrophy (FPLD). Targeting apolipoprotein C3 (apoC3) offers the ability to increase clearance of chylomicrons and other triglyceride-rich lipoproteins. Volanesorsen is an antisense oligonucleotide (ASO) inhibitor of apoC3, which reduces TG levels by 70–80% which has been shown also to reduce rates of pancreatitis and improve well-being in FCS and reduce TGs and improve insulin resistance in FPLD. It is now undergoing licensing and payer reviews. Further developments of antisense technology including small interfering RNA therapy to apoC3 as well as other approaches to modulating triglycerides are in development for this rare disorder.

Targeting apoC-III and ANGPTL3 in the treatment of hypertriglyceridemia

INTRODUCTION

The prevalence of hypertriglyceridemia (HTG) is increasing. Elevated triglyceride (TG) levels are associated with an increased cardiovascular disease (CVD) risk. Moreover, severe HTG results in an elevated risk of pancreatitis, especially in severe HTG with an up to 350-fold increased risk. Both problems emphasize the clinical need for effective TG lowering.

AREAS COVERED

The purpose of this review is to discuss the currently available therapies and to elaborate the most promising novel therapeutics for TG lowering.

EXPERT OPINION

Conventional lipid lowering strategies do not efficiently lower plasma TG levels, leaving a residual CVD and pancreatitis risk. Both apolipoprotein C-III (apoC-III) and angiopoietin-like 3 (ANGPTL3) are important regulators in TG-rich lipoprotein (TRL) metabolism. Several novel agents targeting these linchpins have ended phase II/III trials. Volanesorsen targeting apoC-III has shown reductions in plasma TG levels up to 90%. Multiple ANGPLT3 inhibitors (evinacumab, IONIS-ANGPTL3-L_Rx, ARO-ANG3) effectuate TG reductions up to 70% with concomitant potent reduction in all other apoB containing lipoprotein fractions. We expect these therapeutics to become players in the treatment for (especially) severe HTG in the near future.

Regulation of lipoprotein lipase-mediated lipolysis of triglycerides

PURPOSE OF REVIEW

To discuss the recent developments in structure, function and physiology of lipoprotein lipase (LpL) and the regulators of LpL, which are being targeted for therapy.

RECENT FINDINGS

Recent studies have revealed the long elusive crystal structure of LpL and its interaction with glycosylphosphatidylinositol anchored high-density lipoprotein binding protein 1 (GPIHBP1). New light has been shed on LpL being active as a monomer, which brings into questions previous thinking that LpL inhibitors like angiopoietin-like 4 (ANGPTL4) and stabilizers like LMF1 work on disrupting or maintaining LpL in dimer form. There is increasing pharmaceutical interest in developing targets to block LpL inhibitors like ANGPTL3. Other approaches to reducing circulating triglyceride levels have been using an apoC2 mimetic and reducing apoC3.

SUMMARY

Lipolysis of triglyceride-rich lipoproteins by LpL is a central event in lipid metabolism, releasing fatty acids for uptake by tissues and generating low-density lipoprotein and expanding high-density lipoprotein. Recent mechanistic insights into the structure and function of LpL have added to our understanding of triglyceride metabolism. This has also led to heightened interest in targeting its posttranslational regulators, which can be the next generation of lipid-lowering agents used to prevent hypertriglyceridemic pancreatitis and, hopefully, cardiovascular disease.

Apolipoprotein C-II: the re-emergence of a forgotten factor

PURPOSE OF REVIEW

Apolipoprotein C-II (apoC-II) is a critical cofactor for the activation of lipoprotein lipase (LPL), a plasma enzyme that hydrolyzes triglycerides (TG) on TG-rich lipoproteins (TRL). Although apoC-II was first discovered nearly 50 years ago, there is renewed interest in it because of the recent efforts to develop new drugs for the treatment of hypertriglyceridemia (HTG). The main topic of this review will be the development of apoC-II mimetic peptides as a possible new therapy for cardiovascular disease.

RECENT FINDINGS

We first describe the biochemistry of apoC-II and its role in TRL metabolism. We then review the clinical findings of HTG, particularly those related to apoC-II deficiency, and how TG metabolism relates to the development of atherosclerosis. We next summarize the current efforts to develop new drugs for HTG. Finally, we describe recent efforts to make small synthetic apoC-II mimetic peptides for activation of LPL and how these peptides unexpectedly have other mechanisms of action mostly related to the antagonism of the TG-raising effects of apoC-III.

SUMMARY

The role of apoC-II in TG metabolism is reviewed, as well as recent efforts to develop apoC-II mimetic peptides into a novel therapy for HTG.

Subcutaneous Administration of Apolipoprotein J-Derived Mimetic Peptide d-[113-122]apoJ Improves LDL and HDL Function and Prevents Atherosclerosis in LDLR-KO Mice

Mimetic peptides are potential therapeutic agents for atherosclerosis. d-[113–122]apolipoprotein (apo) J (d-[113–122]apoJ) is a 10-residue peptide that is predicted to form a class G* amphipathic helix 6 from apoJ; it shows anti-inflammatory and anti-atherogenic properties. In the present study, we analyzed the effect of d-[113–122]apoJ in low-density lipoprotein receptor knockout mice(LDLR-KO) on the development of atherosclerosis and lipoprotein function. Fifteen-week-old female LDLR-KO mice fed an atherogenic Western-type diet were treated for eight weeks with d-[113–122]apoJ peptide, a scrambled peptide, or vehicle. Peptides were administered subcutaneously three days per week (200 µg in 100 µL of saline). After euthanasia, blood and hearts were collected and the aortic arch was analyzed for the presence of atherosclerotic lesions. Lipoproteins were isolated and their composition and functionality were studied. The extent of atherosclerotic lesions was 43% lower with d-[113–122]apoJ treatment than with the vehicle or scramble. The lipid profile was similar between groups, but the high-density lipoprotein (HDL) of d-[113–122]apoJ-treated mice had a higher antioxidant capacity and increased ability to promote cholesterol efflux than the control group. In addition, low-density lipoprotein (LDL) from d-[113–122]apoJ-treated mice was more resistant to induced aggregation and presented lower electronegativity than in mice treated with d-[113–122]apoJ. Our results demonstrate that the d-[113–122]apoJ peptide prevents the extent of atherosclerotic lesions, which could be partially explained by the improvement of lipoprotein functionality.

Higher ANGPTL3, apoC-III, and apoB48 dyslipidemia, and lower lipoprotein lipase concentrations are associated with dysfunctional visceral fat in adolescents with obesity

BACKGROUND

We hypothesized that adolescents with obesity have higher remnant B48 concentrations associated with lipoprotein lipase dysregulation.

METHODS

Cross-sectional study of 32 adolescents with obesity and 27 control subjects.

RESULTS

As compared to lean controls, obese participants showed 35% higher concentrations of apoB48: 3.60 (2.93-4.30) vs 2.65 (1.64-3.68) ng/ml; 28% of apoC-III: (72.7 (58.6-89.7) vs 56.9 (44.8-79.8 ug/ml and 17% ANGPTL 3: (72.2 ± 20.2 vs 61.2 ± 19.2 ng/ml). This was accompanied by a 33% reduction in LPL: 13.1 ± 5.1 vs 18.9 ± 4.7 ng/ml. Obese participants had 25% lower adiponectin 2.9 (1.9-3.8) vs 4.4 (3.2.-5.2) μg/ml; 260% higher leptin 25.7 (11.2-44.8) vs 9.3 (2.8-20.7) ng/ml ^c and 83% higher Il-6: 2.2 (1.3-5.4) vs 1.2 (0.8-1.4) pg/ml. ApoC-III and ANGPTL3 correlated positively with VAI; ANGPTL3 negatively with HDL-C; LDL size and VLDL-C. ApoB48 correlated negatively with LDL-C.

CONCLUSIONS

Adolescents with obesity show higher ANGPTL3 compounded with increased apoC-III associated with increased CR and lower LPL mass. This is associated with inflammation and visceral fat. The significance of these findings resides in that they shed light on a mechanism for TRL dyslipidemia in adolescents: increased LPL inhibition impairs VLDL and chylomicron catabolism leading to atherogenic remnants.

Incorporation of α-methylated amino acids into Apolipoprotein A-I mimetic peptides improves their helicity and cholesterol efflux potential

Apolipoprotein A-I (ApoA-I) mimetic peptides are potential therapeutic agents for promoting the efflux of excess cellular cholesterol, which is dependent upon the presence of an amphipathic helix. Since α-methylated Ala enhances peptide helicity, we hypothesized that incorporating other types of α-methylated amino acids into ApoA-I mimetic peptides may also increase their helicity and cholesterol efflux potential. The last helix of apoA-I, peptide 'A' (VLESFKVSFLSALEEYTKKLNT), was used to design peptides containing a single type of α-methylated amino acid substitution (Ala/A_α, Glu/D_α, Lys/K_α, Leu/L_α), as well as a peptide containing both α-methylated Lys and Leu (6_α). Depending on the specific residue, the α-helical content as measured by CD-spectroscopy and calculated hydrophobic moments were sometimes higher for peptides containing other types of α-methylated amino acids than those with α-methylated Ala. In ABCA1-transfected cells, cholesterol efflux to the peptides showed the following order of potency: 6_α>K_α≈L_α≈A_α≫D_α≈A. In general, α-methylated peptides were resistant to proteolysis, but this varied depending on the type of protease and specific amino acid substitution. In summary, increased helicity and amphilicity due to α-methylated amino acid substitutions in ApoA-I mimetic peptides resulted in improved cholesterol efflux capacity and resistance to proteolysis, indicating that this modification may be useful in the future design of therapeutic ApoA-I mimetic peptides.