Missense mutation in APOC3 within the C-terminal lipid binding domain of human ApoC-III results in impaired assembly and secretion of triacylglycerol-rich very low density lipoproteins: evidence that ApoC-III plays a major role in the formation of lipid precursors within the microsomal lumen

ApoC-III proteoforms are associated with better lipid, inflammatory, and glucose profiles independent of total apoC-III

BACKGROUND

Apolipoprotein (apo) C-III is involved in several processes that increase triglyceride levels, inflammation, and insulin resistance. Four of its proteoforms have been the focus of several studies and have shown differential associations with cardiovascular risk biomarkers, mostly lipids. However, there are other proteoforms of apoC-III that have not yet been investigated in detail. The aim of this study was to evaluate the associations of seven apoC-III proteoforms with a comprehensive set of biomarkers, including lipid metabolism, inflammation, and glucose homeostasis.

METHODS

Seven apoC-III proteoforms (apoC-III0a, apoC-III0b, apoC-III1, apoC-III1d, apoC-III2, apoC-III2d, and apoC-III0f) were measured using a mass spectrometry immunoassay in 875 participants from the cross-sectional study of the Di@bet.es cohort. The complete lipoprotein profile was obtained via the Liposcale test, and the proton nuclear magnetic resonance (1H-NMR)-assessed glycoprotein signals were also obtained as biomarkers of inflammation.

RESULTS

Three proteoform ratios (apoC-III2d, apoC-III2, and apoC-III0f normalized to apoC-III1) showed protective associations with most of the cardiovascular risk biomarkers in comparison with total apoC-III in linear regression models and were negatively associated with triglycerides (β=-0.173, p < 0.001; β=-0.297, p < 0.001; β=-0.223, p = 0.002), very low-density (VLDL) particle concentration (β=-0.133, p < 0.001; β=-0.265, p < 0.001; β=-0.203, p < 0.001), GlycA (β=-0.148, p < 0.001; β=-0.263, p < 0.001; β=-0.211, p < 0.001) and homeostatic model assessment of insulin resistance (HOMA-IR) (β=-0.096, p = 0.003; β=-0.199, p < 0.001; β=-0.114, p = 0.002). These associations were partly independent of total apoC-III concentrations. Participants with high levels of these proteoforms had a lower prevalence of cardiometabolic disorders, such as type 2 diabetes (p = 0.022), obesity (p = 0.001), and metabolic syndrome (p = 0.013).

CONCLUSIONS

While apoC-III is positively associated with biomarkers of cardiometabolic risk, the proportions of three apoC-III proteoforms show opposite associations, independent of total apoC-III concentrations. Measuring not only apoC-III but also the proportions of apoC-III proteoforms can provide valuable information since individuals with similar levels of total apoC-III could display opposite lipid profiles depending on the proportion of apoC-III proteoforms.

Dysfunctional VLDL metabolism in MASLD

Lipidomics has unveiled the intricate human lipidome, emphasizing the extensive diversity within lipid classes in mammalian tissues critical for cellular functions. This diversity poses a challenge in maintaining a delicate balance between adaptability to recurring physiological changes and overall stability. Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD), linked to factors such as obesity and diabetes, stems from a compromise in the structural and functional stability of the liver within the complexities of lipid metabolism. This compromise inaccurately senses an increase in energy status, such as during fasting-feeding cycles or an upsurge in lipogenesis. Serum lipidomic studies have delineated three distinct metabolic phenotypes, or "metabotypes" in MASLD. MASLD-A is characterized by lower very low-density lipoprotein (VLDL) secretion and triglyceride (TG) levels, associated with a reduced risk of cardiovascular disease (CVD). In contrast, MASLD-C exhibits increased VLDL secretion and TG levels, correlating with elevated CVD risk. An intermediate subtype, with a blend of features, is designated as the MASLD-B metabotype. In this perspective, we examine into recent findings that show the multifaceted regulation of VLDL secretion by S-adenosylmethionine, the primary cellular methyl donor. Furthermore, we explore the differential CVD and hepatic cancer risk across MASLD metabotypes and discuss the context and potential paths forward to gear the findings from genetic studies towards a better understanding of the observed heterogeneity in MASLD.

Impaired Hepatic Very Low-Density Lipoprotein Secretion Promotes Tumorigenesis and Is Accelerated with Fabp1 Deletion

Genetic polymorphisms that impair very low-density lipoprotein (VLDL) secretion are linked to hepatic steatosis, fibrosis, and hepatocellular cancer. Liver-specific deletion of microsomal triglyceride transfer protein (Mttp-LKO) impairs VLDL assembly, promoting hepatic steatosis and fibrosis, which are attenuated in Mttp-LKO X Fabp1-null [Fabp1/Mttp double knockout (DKO)] mice. The current study examined the impact of impaired VLDL secretion in Mttp-LKO mice on hepatocellular cancer incidence and progression in comparison to Fabp1/Mttp DKO mice. Diethylnitrosamine-treated Mttp-LKO mice exhibited steatosis with increased tumor burden compared with flox controls, whereas diethylnitrosamine-treated Fabp1/Mttp DKO mice exhibited a paradoxical increase in tumor burden and >50% mortality by 50 weeks. Serum high-density lipoprotein cholesterol was elevated in both Mttp-LKO and Fabp1/Mttp DKO mice, with increased intratumoral expression of apolipoprotein A1 and apolipoprotein E. Lipidomic surveys revealed progressive enrichment in distinct triglyceride species in livers from Mttp-LKO mice with further enrichment in Fabp1/Mttp DKO mice. RNA sequencing revealed mRNA changes suggesting altered monocarboxylic acid use and increased aerobic glycolysis, whereas hepatocytes from Fabp1/Mttp DKO mice exhibited increased capacity to use glucose and glutamine. These metabolic shifts were accompanied by reduced expression of HNF1 homeobox A (HNF1a), which correlated with tumor burden. Taken together, these findings demonstrate that hepatic tumorigenesis is increased in mice with impaired VLDL secretion and further accelerated via pathways including altered fatty acid compartmentalization and shifts in hepatic energy use.

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.

FoxO6-mediated ApoC3 upregulation promotes hepatic steatosis and hyperlipidemia in aged rats fed a high-fat diet

FoxO6, an identified factor, induces hyperlipidemia and hepatic steatosis during aging by activating hepatic lipoprotein secretion and lipogenesis leading to increased ApoC3 concentrations in the bloodstream. However, the intricate mechanisms underlying hepatic steatosis induced by elevated FoxO6 under hyperglycemic conditions remain intricate and require further elucidation. In order to delineate the regulatory pathway involving ApoC3 controlled by FoxO6 and its resultant functional impacts, we employed a spectrum of models including liver cell cultures, aged rats subjected to HFD, transgenic mice overexpressing FoxO6 (FoxO6-Tg), and FoxO6 knockout mice (FoxO6-KO). Our findings indicate that FoxO6 triggered ApoC3-driven lipid accumulation in the livers of aged rats on an HFD and in FoxO6-Tg, consequently leading to hepatic steatosis and hyperglycemia. Conversely, the absence of FoxO6 attenuated the expression of genes involved in lipogenesis, resulting in diminished hepatic lipid accumulation and mitigated hyperlipidemia in murine models. Additionally, the upregulation of FoxO6 due to elevated glucose levels led to increased ApoC3 expression, consequently instigating cellular triglyceride mediated lipid accumulation. The transcriptional activation of FoxO6 induced by both the HFD and high glucose levels resulted in hepatic steatosis by upregulating ApoC3 and genes associated with gluconeogenesis in aged rats and liver cell cultures. Our conclusions indicate that the upregulation of ApoC3 by FoxO6 promotes the development of hyperlipidemia, hyperglycemia, and hepatic steatosis in vivo, and in vitro. Taken together, our findings underscore the significance of FoxO6 in driving hyperlipidemia and hepatic steatosis specifically under hyperglycemic states by enhancing the expression of ApoC3 in aged rats.

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.

Unanticipated Enhancement of Intestinal TG Output by Apoc3 ASO Inhibition

BACKGROUND

The objective of this study was to investigate whether apoC3 (apolipoprotein C3) inhibition with an antisense oligonucleotide (ASO) modulates intestinal triglyceride secretion.

METHODS

Sprague-Dawley rats were treated with subcutaneous injections of apoC3 ASO 25 mg/kg twice weekly or inactive ASO for 4 weeks before the assessment of lymph flow, triglyceride and apoB48 (apolipoprotein B48) appearance in the lymph. Rats were surgically implanted with catheters in the mesenteric lymph duct and duodenum. Following an overnight fast, an intraduodenal lipid bolus (1.5-mL intralipid) was administered. Lymph fluid was collected for the following 4 hours to compare effects on lymph flow, lymph triglyceride and apoB48 concentration, and secretion. To assess suppression of apoC3 expression and protein abundance by apoC3 ASO compared with inactive ASO (placebo), intestinal and hepatic tissues were collected from a subset of animals before (fasting) and after an enteral lipid bolus (post-lipid).

RESULTS

ApoC3 ASO significantly reduced apoC3 mRNA expression in the liver compared with inactive ASO (fasting: 42%, P=0.0048; post-lipid: 66%, P<0.001) and in the duodenum (fasting: 29%, P=0.0424; post-lipid: 53%, P=0.0120). As expected, plasma triglyceride also decreased significantly (fasting: 74%, P<0.001; post-lipid: 33%, P=0.0276). Lymph flow and cumulative lymph volume remained unchanged following apoC3 ASO therapy; however, lymph triglyceride, but not apoB48 output, increased by 38% (ANOVA, P<0.001). Last, no changes were observed in stool triglyceride, intestinal fat (quantified via oil red O staining), and expression of mRNAs involved in triglyceride synthesis, lipid droplet formation, and chylomicron transport and secretion.

CONCLUSIONS

Despite the marked reduction in plasma triglyceride concentration that occurs with apoC3 ASO inhibition, intestinal triglyceride output surprisingly increased rather than decreased. These data demonstrate that the reduction of intestinal triglyceride output does not contribute to the potent plasma triglyceride-lowering observed with this novel therapy for hypertriglyceridemia. Further studies are required to explore the mechanism of this intestinal effect.

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.

Obstructive Sleep Apnoea and Lipid Metabolism: The Summary of Evidence and Future Perspectives in the Pathophysiology of OSA-Associated Dyslipidaemia

Obstructive sleep apnoea (OSA) is associated with cardiovascular and metabolic comorbidities, including hypertension, dyslipidaemia, insulin resistance and atherosclerosis. Strong evidence suggests that OSA is associated with an altered lipid profile including elevated levels of triglyceride-rich lipoproteins and decreased levels of high-density lipoprotein (HDL). Intermittent hypoxia; sleep fragmentation; and consequential surges in the sympathetic activity, enhanced oxidative stress and systemic inflammation are the postulated mechanisms leading to metabolic alterations in OSA. Although the exact mechanisms of OSA-associated dyslipidaemia have not been fully elucidated, three main points have been found to be impaired: activated lipolysis in the adipose tissue, decreased lipid clearance from the circulation and accelerated de novo lipid synthesis. This is further complicated by the oxidisation of atherogenic lipoproteins, adipose tissue dysfunction, hormonal changes, and the reduced function of HDL particles in OSA. In this comprehensive review, we summarise and critically evaluate the current evidence about the possible mechanisms involved in OSA-associated dyslipidaemia.

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.

Metabolic subtypes of patients with NAFLD exhibit distinctive cardiovascular risk profiles

BACKGROUND AND AIMS

We previously identified subsets of patients with NAFLD with different metabolic phenotypes. Here we align metabolomic signatures with cardiovascular disease (CVD) and genetic risk factors.

APPROACH AND RESULTS

We analyzed serum metabolome from 1154 individuals with biopsy-proven NAFLD, and from four mouse models of NAFLD with impaired VLDL-triglyceride (TG) secretion, and one with normal VLDL-TG secretion. We identified three metabolic subtypes: A (47%), B (27%), and C (26%). Subtype A phenocopied the metabolome of mice with impaired VLDL-TG secretion; subtype C phenocopied the metabolome of mice with normal VLDL-TG; and subtype B showed an intermediate signature. The percent of patients with NASH and fibrosis was comparable among subtypes, although subtypes B and C exhibited higher liver enzymes. Serum VLDL-TG levels and secretion rate were lower among subtype A compared with subtypes B and C. Subtype A VLDL-TG and VLDL-apolipoprotein B concentrations were independent of steatosis, whereas subtypes B and C showed an association with these parameters. Serum TG, cholesterol, VLDL, small dense LDL5,6 , and remnant lipoprotein cholesterol were lower among subtype A compared with subtypes B and C. The 10-year high risk of CVD, measured with the Framingham risk score, and the frequency of patatin-like phospholipase domain-containing protein 3 NAFLD risk allele were lower in subtype A.

CONCLUSIONS

Metabolomic signatures identify three NAFLD subgroups, independent of histological disease severity. These signatures align with known CVD and genetic risk factors, with subtype A exhibiting a lower CVD risk profile. This may account for the variation in hepatic versus cardiovascular outcomes, offering clinically relevant risk stratification.

Safety and efficacy of therapies for chylomicronemia

INTRODUCTION

Primary chylomicronemia is characterized by pathological accumulation of chylomicrons in the plasma causing severe hypertriglyceridemia, typically >10 mmol/L (>875 mg/dL). Patients with the ultra-rare familial chylomicronemia syndrome (FCS) subtype completely lack lipolytic capacity and respond minimally to traditional triglyceride-lowering therapies. The mainstay of treatment is a low-fat diet, which is difficult to follow and compromises quality of life. New therapies are being developed primarily to prevent episodes of life-threatening acute pancreatitis.

AREAS COVERED

Antagonists of apolipoprotein (apo) C-III, such as the antisense oligonucleotide (ASO) volanesorsen, significantly reduce triglyceride levels in chylomicronemia. However, approval of and access to volanesorsen are restricted since a substantial proportion of treated FCS patients developed thrombocytopenia. Newer apo C-III antagonists, namely, the ASO olezarsen (formerly AKCEA-APOCIII-LRx) and short interfering RNA (siRNA) ARO-APOC3, appear to show efficacy with less risk of thrombocytopenia. Potential utility of antagonists of angiopoietin-like protein 3 (ANGPTL3) such as evinacumab and the siRNA ARO-ANG3 in subtypes of chylomicronemia remains to be defined.

EXPERT OPINION

Emerging pharmacologic therapies for chylomicronemia show promise, particularly apo C-III antagonists. However, these treatments are still investigational. Further study of their efficacy and safety in patients with both rare FCS and more common multifactorial chylomicronemia is needed.

Plasma proteomics reveals crosstalk between lipid metabolism and immunity in dairy cows receiving essential fatty acids and conjugated linoleic acid

Essential fatty acids (EFA) and conjugated linoleic acids (CLA) are unsaturated fatty acids with immune-modulatory effects, yet their synergistic effect is poorly understood in dairy cows. This study aimed at identifying differentially abundant proteins (DAP) and their associated pathways in dairy cows supplied with a combination of EFA and CLA during the transition from antepartum (AP) to early postpartum (PP). Sixteen Holstein cows were abomasally infused with coconut oil as a control (CTRL) or a mixture of EFA (linseed + safflower oil) and CLA (Lutalin, BASF) (EFA + CLA) from − 63 to + 63 days relative to parturition. Label-free quantitative proteomics was performed on plasma samples collected at days − 21, + 1, + 28, and + 63. During the transition time, DAP, consisting of a cluster of apolipoproteins (APO), including APOE, APOH, and APOB, along with a cluster of immune-related proteins, were related to complement and coagulation cascades, inflammatory response, and cholesterol metabolism. In response to EFA + CLA, specific APO comprising APOC3, APOA1, APOA4, and APOC4 were increased in a time-dependent manner; they were linked to triglyceride-enriched lipoprotein metabolisms and immune function. Altogether, these results provide new insights into metabolic and immune adaptation and crosstalk between them in transition dairy cows divergent in EFA + CLA status.

Is Apo-CIII the new cardiovascular target? An analysis of its current clinical and dietetic therapies

AIMS

Recently, Apolipoprotein CIII (Apo-CIII) has gained remarkable attention since its overexpression has been strongly correlated to cardiovascular disease (CVD) occurrence. The aim of this review was to summarize the latest findings of Apo-CIII as a CVDs and diabetes risk factor, as well as the plausible mechanisms involved in the development of these pathologies, with particular emphasis on current clinical and dietetic therapies.

DATA SYNTHESIS

Apo-CIII is a small protein (∼8.8 kDa) that, among other functions, inhibits lipoprotein lipase, a key enzyme in lipid metabolism. Apo-CIII plays a fundamental role in the physiopathology of atherosclerosis, type-1, and type-2 diabetes. Apo-CIII has become a potential clinical target to tackle these multifactorial diseases. Dietetic (omega-3 fatty acids, stanols, polyphenols, lycopene) and non-dietetic (fibrates, statins, and antisense oligonucleotides) therapies have shown promising results to regulate Apo-CIII and triglyceride levels. However, more information from clinical trials is required to validate it as a new target for atherosclerosis and diabetes types 1 and 2.

CONCLUSIONS

There are still several pathways involving Apo-CIII regulation that might be affected by bioactive compounds that need further research. The mechanisms that trigger metabolic responses following bioactive compounds consumption are mainly related to higher LPL expression and PPARα activation, although the complete pathways are yet to be elucidated.

Volanesorsen for treatment of familial chylomicronemia syndrome

INTRODUCTION

Familial chylomicronemia syndrome (FCS) is a rare subtype of severe hypertriglyceridemia that affects ~1 in 100, 000 to 1,000,000 individuals. The major risk to health is acute pancreatitis. FCS is defined by biallelic loss-of-function mutations in one of five canonical genes that encode proteins critical to lipolysis of large triglyceride-rich lipoprotein particles. Unlike the vast majority of patients with severe hypertriglyceridemia, FCS patients lack any lipolytic capacity and are thus resistant to standard medications.

AREAS COVERED

This review focuses on a mechanism that effectively reduces elevated triglyceride levels in FCS, namely interference of synthesis of apolipoprotein (apo) C-III. Volanesorsen is an antisense RNA drug administered subcutaneously that knocks down apo C-III, resulting in dramatic reductions in triglyceride levels both in FCS patients and in the wider population of subjects with severe hypertriglyceridemia.

EXPERT OPINION

Volanesorsen is a highly effective treatment to reduce elevated triglycerides in FCS patients, providing proof-of-concept of the validity of targeting apo C-III. However, off target effects of volanesorsen, including thrombocytopenia, may ultimately limit its use. Nonetheless, building on the knowledge derived from the volanesorsen experience, there is intensified interest in promising newer agents that also target apo C-III but have technical modifications that limit potential off target adverse effects.

The interplay between host cellular and gut microbial metabolism in NAFLD development and prevention

Metabolism regulation centred on insulin resistance is increasingly important in nonalcoholic fatty liver disease (NAFLD). This review focuses on the interactions between the host cellular and gut microbial metabolism during the development of NAFLD. The cellular metabolism of essential nutrients, such as glucose, lipids and amino acids, is reconstructed with inflammation, immune mechanisms and oxidative stress, and these alterations modify the intestinal, hepatic and systemic environments, and regulate the composition and activity of gut microbes. Microbial metabolites, such as short-chain fatty acids, secondary bile acids, protein fermentation products, choline and ethanol and bacterial toxicants, such as lipopolysaccharides, peptidoglycans and bacterial DNA, play vital roles in NAFLD. The microbe-metabolite relationship is crucial for the modulation of intestinal microbial composition and metabolic activity. The intestinal microbiota and their metabolites participate in epithelial cell metabolism via a series of cell receptors and signalling pathways and remodel the metabolism of various cells in the liver via the gut-liver axis. Microbial metabolic manipulation is a promising strategy for NAFLD prevention, but larger-sampled clinical trials are required for future application.

ApoCIII: A multifaceted protein in cardiometabolic disease

ApoCIII has a well-recognized role in triglyceride-rich lipoproteins metabolism. A considerable amount of data has clearly highlighted that high levels of ApoCIII lead to hypertriglyceridemia and, thereby, may influence the risk of cardiovascular disease. However, recent findings indicate that ApoCIII might also act beyond lipid metabolism. Indeed, ApoCIII has been implicated in other physiological processes such as glucose homeostasis, monocyte adhesion, activation of inflammatory pathways, and modulation of the coagulation cascade. As the inhibition of ApoCIII is emerging as a new promising therapeutic strategy, the complete understanding of multifaceted pathophysiological role of this apoprotein may be relevant. Therefore, the purpose of this work is to review available evidences not only related to genetics and biochemistry of ApoCIII, but also highlighting the role of this apoprotein in triglyceride and glucose metabolism, in the inflammatory process and coagulation cascade as well as in cardiovascular disease.

Methionine- and Choline-Deficient Diet Enhances Adipose Lipolysis and Leptin Release in aP2-Cre Fatp4-Knockout Mice

SCOPE

Inadequate intake of choline commonly leads to liver diseases. Methionine- and choline-deficient diets (MCDD) induce fatty liver in mice which is partly mediated by triglyceride (TG) lipolysis in white adipose tissues (WATs). Because Fatp4 knockdown has been shown to increase adipocyte lipolysis in vitro, here, the effects of MCDD on WAT lipolysis in aP2-Cre Fatp4-knockout (Fatp4^A-/- ) mice are determined.

METHODS AND RESULTS

Isolated WATs of Fatp4^A-/- mice exposed to MCD medium show an increase in lipolysis, and the strongest effect is noted on glycerol release from subcutaneous fat. Fatp4^A-/- mice fed with MCDD for 4 weeks show an increase in serum glycerol, TG, and leptin levels associated with the activation of hormone-sensitive lipase in subcutaneous fat. Chow-fed Fatp4^A-/- mice also show an increase in serum leptin and very-low-density lipoproteins as well as liver phosphatidylcholine and sphingomyelin levels. Both chow- and MCDD-fed Fatp4^A-/- mice show a decrease in serum ketone and WAT sphingomyelin levels which supports a metabolic shift to TG for subsequent WAT lipolysis CONCLUSIONS: Adipose Fatp4 deficiency leads to TG lipolysis and leptin release, which are exaggerated by MCDD. The data imply hyperlipidemia risk by a low dietary choline intake and gene mutations that increase adipose TG levels.

The relation between VLDL-cholesterol and risk of cardiovascular events in patients with manifest cardiovascular disease

INTRODUCTION

Apolipoprotein B containing lipoproteins are atherogenic. There is evidence that with low plasma low density lipoprotein cholesterol (LDL-C) levels residual vascular risk might be caused by triglyceride rich lipoproteins such as very-low density lipoproteins (VLDL), chylomicrons and their remnants. We investigated the relationship between VLDL-cholesterol (VLDL-C) and recurrent major adverse cardiovascular events (MACE), major adverse limb events (MALE) and all-cause mortality in a cohort of patients with cardiovascular disease.

METHODS

Prospective cohort study in 8057 patients with cardiovascular disease from the UCC-SMART study. The relation between calculated VLDL-C levels and the occurrence of MACE, MALE and all-cause mortality was analyzed with Cox regression models.

RESULTS

Patients mean age was 60 ± 10 years, 74% were male, 4894 (61%) had coronary artery disease, 2445 (30%) stroke, 1425 (18%) peripheral arterial disease and 684 (8%) patients had an abdominal aorta aneurysm at baseline. A total of 1535 MACE, 571 MALE and 1792 deaths were observed during a median follow up of 8.2 years (interquartile range 4.512.2). VLDL-C was not associated with risk of MACE or all-cause mortality. In the highest quartile of VLDL-C the risk was higher for major adverse limb events (MALE) (HR 1.49; 95%CI 1.16-1.93) compared to the lowest quartile, after adjustment for confounders including LDL-C and lipid lowering medication.

CONCLUSION

In patients with clinically manifest cardiovascular disease plasma VLDL-C confers an increased risk for MALE, but not for MACE and all-cause mortality, independent of established risk factors including LDL-C and lipid-lowering medication.

Apolipoprotein CIII Deficiency Protects Against Atherosclerosis in Knockout Rabbits

OBJECTIVE

Apo (apolipoprotein) CIII mediates the metabolism of triglyceride (TG)-rich lipoproteins. High levels of plasma apoCIII are positively correlated with the plasma TG levels and increase the cardiovascular risk. However, whether apoCIII is directly involved in the development of atherosclerosis has not been fully elucidated. Approach and Results: To examine the possible roles of apoCIII in lipoprotein metabolism and atherosclerosis, we generated apoCIII KO (knockout) rabbits using ZFN (zinc finger nuclease) technique. On a normal standard diet, apoCIII KO rabbits exhibited significantly lower plasma levels of TG than those of WT (wild type) rabbits while total cholesterol and HDL (high-density lipoprotein) cholesterol levels were unchanged. Analysis of lipoproteins isolated by sequential ultracentrifugation revealed that reduced plasma TG levels in KO rabbits were accompanied by prominent reduction of VLDLs (very-low-density lipoproteins) and IDLs (intermediate-density lipoproteins). In addition, KO rabbits showed faster TG clearance rate after intravenous fat load than WT rabbits. On a cholesterol-rich diet, KO rabbits exhibited constantly and significantly lower levels of plasma total cholesterol and TG than WT rabbits, which was caused by a remarkable reduction of β-VLDLs-the major atherogenic lipoproteins. β-VLDLs of KO rabbits showed higher uptake by cultured hepatocytes and were cleared faster from the circulation than β-VLDLs isolated from WT rabbits. Both aortic and coronary atherosclerosis was significantly reduced in KO rabbits compared with WT rabbits.

CONCLUSIONS

These results indicate that apoCIII deficiency facilitates TG-rich lipoprotein catabolism, and therapeutic inhibition of apoCIII expression may become a novel means not only for the treatment of hyperlipidemia but also for atherosclerosis.

Biotechnology Approaches for the Treatment of Dyslipidemia

BACKGROUND

Despite advances in the development of lipid-lowering therapies, clinical trials have shown that a significant residual risk of cardiovascular disease persists. Specifically, new drugs are needed for non-responding or statin-intolerant subjects or patients considered at very high risk for cardiovascular events even though are already on treatment with the best standard of care.

RESULTS AND CONCLUSIONS

Besides, genetic and epidemiological studies and Mendelian randomization analyses have strengthened the linear correlation between the concentration of low-density lipoprotein cholesterol (LDL-C) and the incidence of cardiovascular events and highlighted various novel therapeutic targets. This review describes the novel strategies to reduce the levels of LDL-C, non-HDL-C, triglyceride, apolipoprotein B, and Lp(a), focusing on those developed using biotechnology-based strategies.

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.

ApoE and apoC-III-defined HDL subtypes: a descriptive study of their lecithin cholesterol acyl transferase and cholesteryl ester transfer protein content and activity

Background

The functionality of high-density lipoproteins (HDL) is a better cardiovascular risk predictor than HDL concentrations. One of the key elements of HDL functionality is its apolipoprotein composition. Lecithin-cholesterol acyl transferase (LCAT) and cholesterol-ester transfer protein (CETP) are enzymes involved in HDL-mediated reverse cholesterol transport. This study assessed the concentration and activity of LCAT and CETP in HDL subspecies defined by their content of apolipoproteins E (apoE) and C-III (apoC-III) in humans.

Methods

Eighteen adults (ten women and eight men, mean age 55.6, BMI 26.9 Kg/m², HbA1c 5.4%) were studied. HDL from each participant were isolated and divided into four subspecies containing respectively: No apoE and no apoC-III (E-C-), apoE but not apoC-III (E + C-), apoC-III but no apoE (E-C+) and both apoE and apoC-III (E + C+). The concentration and enzymatic activity of LCAT and CETP were measured within each HDL subspecies using immunoenzymatic and fluorometric methods. Additionally, the size distribution of HDL in each apolipoprotein-defined fraction was determined using non-denaturing electrophoresis and anti-apoA-I western blotting.

Results

HDL without apoE or apoC-III was the predominant HDL subtype. The size distribution of HDL was very similar in all the four apolipoprotein-defined subtypes. LCAT was most abundant in E-C- HDL (3.58 mg/mL, 59.6% of plasma LCAT mass), while HDL with apoE or apoC-III had much less LCAT (19.8, 12.2 and 8.37% of plasma LCAT respectively for E + C-, E-C+ and E + C+). LCAT mass was lower in E + C- HDL relative to E-C- HDL, but LCAT activity was similar in both fractions, signaling a greater activity-to-mass ratio associated with the presence of apoE. Both CETP mass and CETP activity showed only slight variations across HDL subspecies. There was an inverse correlation between plasma LCAT activity and concentrations of both E-C+ pre-beta HDL (r = − 0.55, P = 0.017) and E-C- alpha 1 HDL (r = − 0.49, P = 0.041). Conversely, there was a direct correlation between plasma CETP activity and concentrations of E-C+ alpha 1 HDL (r = 0.52, P = 0.025).

Conclusions

The presence of apoE in small HDL is correlated with increased LCAT activity and esterification of plasma cholesterol. These results favor an interpretation that LCAT and apoE interact to enhance anti-atherogenic pathways of HDL.

Nonalcoholic fatty liver disease experiences accumulation of hepatic liquid crystal associated with increasing lipophagy

Background

In the past 30 years, incidences of non-alcoholic fatty liver disease (NAFLD) has risen by 30%. However, there is still no clear mechanism or accurate method of anticipating liver failure. Here we reveal the phase transitions of liquid crystalline qualities in hepatic lipid droplets (HLDs) as a novel method of anticipating prognosis.

Methods

NAFLD was induced by feeding C57BL/6J mice on a high-fat (HiF) diet. These NAFLD livers were then evaluated under polarized microscopy, X-ray diffraction and small-angle scattering, lipid component chromatography analysis and protein expression analysis. Optically active HLDs from mouse model and patient samples were both then confirmed to have liquid crystal characteristics. Liver MAP1LC3A expression was then evaluated to determine the role of autophagy in liquid crystal HLD (LC-HLD) formation.

Results

Unlike the normal diet cohort, HiF diet mice developed NAFLD livers containing HLDs exhibiting Maltese cross birefringence, phase transition, and fluidity signature to liquid crystals. These LC-HLDs transitioned to anisotropic crystal at 0 °C and remain crystalline. Temperature increase to 42 °C causes both liquid crystal and crystal HLDs to convert to isotropic droplet form. These isotropic HLDs successfully transition to anisotropic LC with fast temperature decrease and anisotropic crystal with slow temperature decrease. These findings were duplicated in patient liver. Patient LC-HLDs with no inner optical activity were discovered, hinting at lipid saturation as the mechanism through which HLD acquire LC characteristics. Downregulation of MAP1LC3A in conjunction with increased LC-HLD also implicated autophagy in NAFLD LC-HLD formation.

Conclusions

Increasing concentrations of amphiphilic lipids in HLDs favors organization into alternating hydrophilic and hydrophobic layers, which present as LC-HLDs. Thus, evaluating the extent of liquid crystallization with phase transition in HLDs of NAFLD patients may reveal disease severity and predict impending liver damage.

Sitagliptin improves plasma apolipoprotein profile in type 2 diabetes: A randomized clinical trial of sitagliptin effect on lipid and glucose metabolism (SLIM) study

AIM

This study aims to evaluate the effect of dipeptidyl peptidase-4 inhibitors on lipid metabolism in patients with type 2 diabetes mellitus (T2D).

METHODS

This is a multicenter, open-labeled, randomized controlled study. T2D patients with HbA1c 6.9-8.9% (52-74 mmol/mol) who were under treatment with sulfonylurea were randomly allocated to either the sitagliptin group or the non-sitagliptin group. Glucose and lipid metabolism parameters including apolipoproteins (apo), sterols, and urinary albumin were assessed at baseline, 3, and 6 months of the treatment.

RESULTS

A total of 164 patients completed the 6-month observation (n = 81 for sitagliptin and n = 83 for non-sitagliptin). HbA1c decreased in the sitagliptin group but not in the non-sitagliptin group. Serum TG and total, LDL and HDL cholesterol levels did not change in either group. Apo B-48, apo CII, and apo CIII levels decreased in the sitagliptin group, but not in the non-sitagliptin group. The change in urinary albumin was significantly different between the groups with a preferable change in the sitagliptin group. There were no changes in serum sterols levels in the two groups.

CONCLUSIONS

The treatment of sitagliptin for 6 months improves the metabolism of glucose and chylomicron and reduces plasma levels of atherogenic lipoproteins in patients with T2D.

The exchangeable apolipoproteins in lipid metabolism and obesity

Dyslipidemia, characterized by increased plasma levels of low-density lipoprotein cholesterol (LDL-C), very low-density lipoprotein cholesterol (VLDL-C), triglyceride (TG), and reduced plasma levels of high-density lipoprotein cholesterol (HDL-C), is confirmed as a hallmark of obesity and cardiovascular diseases (CVD), posing serious risks to the future health of humans. Thus, it is important to understand the molecular metabolism of dyslipidemia, which could help reduce the morbidity and mortality of obesity and CVD. Currently, several exchangeable apolipoproteins, such as apolipoprotein A1 (ApoA1), apolipoprotein A5 (ApoA5), apolipoprotein E (ApoE), and apolipoprotein C3 (ApoC3), have been verified to exert vital effects on modulating lipid metabolism and homeostasis both in plasma and in cells, which consequently affect dyslipidemia. In the present review, we summarize the findings of the effect of exchangeable apolipoproteins on affecting lipid metabolism in adipocytes and hepatocytes. Furthermore, we also provide new insights into the mechanisms by which the exchangeable apolipoproteins influence the pathogenesis of dyslipidemia and its related cardio-metabolic disorders.

Recent developments in pharmacotherapy for hypertriglyceridemia: what's the current state of the art?

Introduction: Hypertriglyceridemia is associated with both the development of cardiovascular disease (CVD) when mild-to-moderate and high risk of pancreatitis when more severe. The residual CVD risk after low-density lipoprotein cholesterol (LDL-C) lowering is, in part, attributed to high triglyceride (TG) levels. Therefore, there appears to be a need for effective TG-lowering agents.Areas covered: This review presents the most recent advances in hypertriglyceridemia treatment; specifically, it discusses the results of clinical trials and critically comments on apolipoprotein C-III inhibitors, angiopoietin-like 3 inhibitors, alipogene tiparvovec, pradigastat, pemafibrate and novel formulations of omega-3 fatty acids.Expert opinion: In the era of extreme lowering of LDL-C levels with several agents, there seems to be space for novel therapeutic options to combat parameters responsible for residual CVD risk, among which are elevated TGs. Furthermore, a significant number of individuals have very high TG levels and encounter the risk of acute pancreatitis. The most recently developed TG-lowering drugs appear to have a role in both conditions; the choice is mainly based on baseline TG levels. Dyslipidemia guidelines are likely to change in the near future to include some of these agents. Of course, long-term data regarding their safety and efficacy in terms of CVD outcomes and pancreatitis are warranted.

Sequence analysis and variant identification at the APOC3 gene locus indicates association of rs5218 with BMI in a sample of Kuwaiti's

Background

APOC3 is important in lipid transport and metabolism with limited studies reporting genetic sequence variations in specific ethnic groups. The present study aimed to analyze the full APOC3 sequence among Kuwaiti Arabs and test the association of selected variants with lipid levels and BMI.

Methods

Variants were identified by Sanger sequencing the entire APOC3 gene in 100 Kuwaiti Arabs. Variants and their genotypes were fully characterized and used to construct haplotype blocks. Four variants (rs5128, rs2854117, rs2070668, KUAPOC3N3 g.5196 A > G) were selected for testing association with serum lipid levels and BMI in a cohort (n = 733).

Results

APOC3 sequence (4.3 kb) of a Kuwaiti Arab was deposited in Genbank (accession number KJ437193). Forty-two variants including 3 novels were identified including an “A” insertion at genomic positions 116,700,599–116,700,600 (promoter region) and two substitutions in intron 1 at genomic positions 116,700,819 and 116,701,159. Only three variants, (rs5128, rs2854117, and rs2070668) were analyzed for association of which rs5128 showed a trend for association with increased BMI, TG and VLDL levels that was further investigated using multivariate analysis. A significant association of rs5128 with BMI (p <  0.05) was observed following a dominant genetic model with increased risk by an OR of 4.022 (CI: 1.13–14.30).

Conclusion

The present study is the first to report sequence analysis of APOC3 in an Arab ethnic group. This study supports the inclusion of rs5128 as a marker for assessing genetic risk to dyslipidemia and obesity and the inclusion of the novel variant g.5196 A > G for population stratification of Arabs.

Emerging evidences for the opposite role of apolipoprotein C3 and apolipoprotein A5 in lipid metabolism and coronary artery disease

Apolipoprotein C3 (apoC3) and apolipoprotein A5 (apoA5), encoded by APOA1/C3/A4/A5 gene cluster, are two critical regulators of plasma triglyceride (TG) metabolism. Deficiency of apoC3 or apoA5 led to significant decreased or increased plasma TG levels, respectively. Recent studies indicated apoC3 and apoA5 also played roles in plasma remnant cholesterol, high density lipoprotein (HDL) and hepatic TG metabolisms. Moreover, large scale population genetic studies indicated that loss of function mutations in APOC3 and APOA5 gene conferred decreased and increased risk of coronary artery disease (CAD), respectively. This manuscript mainly reviewed existing evidences suggesting the opposite role of apoC3 and apoA5 in lipid metabolism and CAD risk, and discussed the potential correlation between these two apolipoproteins.

Lipid-Lowering Agents

Several new or emerging drugs for dyslipidemia owe their existence, in part, to human genetic evidence, such as observations in families with rare genetic disorders or in Mendelian randomization studies. Much effort has been directed to agents that reduce LDL (low-density lipoprotein) cholesterol, triglyceride, and Lp[a] (lipoprotein[a]), with some sustained programs on agents to raise HDL (high-density lipoprotein) cholesterol. Lomitapide, mipomersen, AAV8.TBG.hLDLR, inclisiran, bempedoic acid, and gemcabene primarily target LDL cholesterol. Alipogene tiparvovec, pradigastat, and volanesorsen primarily target elevated triglycerides, whereas evinacumab and IONIS-ANGPTL3-L_Rx target both LDL cholesterol and triglyceride. IONIS-APO(a)-L_Rx targets Lp(a).

Biomarkers and subtypes of deranged lipid metabolism in non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a heterogeneous and complex disease that is imprecisely diagnosed by liver biopsy. NAFLD covers a spectrum that ranges from simple steatosis, nonalcoholic steatohepatitis (NASH) with varying degrees of fibrosis, to cirrhosis, which is a major risk factor for hepatocellular carcinoma. Lifestyle and eating habit changes during the last century have made NAFLD the most common liver disease linked to obesity, type 2 diabetes mellitus and dyslipidemia, with a global prevalence of 25%. NAFLD arises when the uptake of fatty acids (FA) and triglycerides (TG) from circulation and de novo lipogenesis saturate the rate of FA β-oxidation and very-low density lipoprotein (VLDL)-TG export. Deranged lipid metabolism is also associated with NAFLD progression from steatosis to NASH, and therefore, alterations in liver and serum lipidomic signatures are good indicators of the disease’s development and progression. This review focuses on the importance of the classification of NAFLD patients into different subtypes, corresponding to the main alteration(s) in the major pathways that regulate FA homeostasis leading, in each case, to the initiation and progression of NASH. This concept also supports the targeted intervention as a key approach to maximize therapeutic efficacy and opens the door to the development of precise NASH treatments.

Apolipoprotein C-III and its defined lipoprotein subspecies in relation to incident diabetes: the Multi-Ethnic Study of Atherosclerosis

AIMS/HYPOTHESIS

Apolipoprotein C-III (apoC-III) is a small proinflammatory protein that may play a key role in diabetes pathophysiology. However, prior observational studies have been limited to predominantly white populations, and the biological links between apoC-III and diabetes, particularly the role of apoC-III on specific lipoprotein particles, are not yet well understood. We therefore investigated associations of total apoC-III and apoC-III-defined lipoprotein subspecies with incident diabetes and glucose metabolism measures in a multi-ethnic cohort.

METHODS

For the current analyses, baseline (2000-2002) plasma total apoC-III and apolipoprotein A-I concentrations of HDL containing or lacking apoC-III were newly measured via sandwich ELISA in 4579 participants from the Multi-Ethnic Study of Atherosclerosis. Multivariable Cox regression was used to examine associations of apolipoproteins with incident diabetes until early 2012 (567 cases), and linear mixed models were used to estimate associations with longitudinally assessed continuous measures of glucose metabolism. Similar exploratory analyses of plasma apolipoprotein B concentrations of LDL and VLDL containing or lacking apoC-III were performed in a subset of participants (LDL, n = 1545; VLDL, n = 1526).

RESULTS

In the overall population, elevated total apoC-III concentrations were associated with a higher rate of diabetes (top vs bottom quintile, HR 1.88; 95% CI 1.42, 2.47; p_trend = 0.0002). ApoC-III-defined HDL subspecies displayed opposing associations with incidence of diabetes (p for heterogeneity = 0.02). While HDL lacking apoC-III was inversely associated with incidence of diabetes (top vs bottom quintile, HR 0.66; 95% CI 0.46, 0.93; p_trend = 0.002), HDL containing apoC-III was not associated (HR 1.11; 95% CI 0.78, 1.58; p_trend = 0.61). Similarly, only HDL lacking apoC-III was beneficially associated with plasma glucose (p_trend = 0.003), HbA_1c (p_trend = 0.04) and insulin sensitivity (p_trend < 0.0001), and higher HDL containing apoC-III was associated with lower insulin sensitivity (p_trend = 0.04). Neither of the apoC-III-defined LDL subspecies was associated with incident diabetes, while VLDL was more strongly associated with the incidence of diabetes when it lacked apoC-III. Further adjustment for plasma triacylglycerols as a potential intermediate attenuated the associations of total apoC-III and apoC-III-defined lipoprotein subspecies. No statistically significant differences were observed across racial/ethnic groups.

CONCLUSIONS/INTERPRETATION

Our findings in a multi-ethnic population support the involvement of apoC-III in the development of diabetes, potentially through its association with circulating triacylglycerols. The presence of apoC-III on HDL also diminished the protective association of HDL with incident diabetes. Further investigation of apoC-III and apoC-III-defined HDL subspecies may inform the development of novel diabetes treatment and prevention strategies.

ApoC-III ASO promotes tissue LPL activity in the absence of apoE-mediated TRL clearance

Hypertriglyceridemia results from accumulation of triglyceride (TG)-rich lipoproteins (TRLs) in the circulation and is associated with increased CVD risk. ApoC-III is an apolipoprotein on TRLs and a prominent negative regulator of TG catabolism. We recently established that in vivo apoC-III predominantly inhibits LDL receptor-mediated and LDL receptor-related protein 1-mediated hepatic TRL clearance and that apoC-III-enriched TRLs are preferentially cleared by syndecan-1 (SDC1). In this study, we determined the impact of apoE, a common ligand for all three receptors, on apoC-III metabolism using apoC-III antisense oligonucleotide (ASO) treatment in mice lacking apoE and functional SDC1 (Apoe^−/−Ndst1^f/fAlb-Cre⁺). ApoC-III ASO treatment significantly reduced plasma TG levels in Apoe^−/−Ndst1^f/fAlb-Cre⁺ mice without reducing hepatic VLDL production or improving hepatic TRL clearance. Further analysis revealed that apoC-III ASO treatment lowered plasma TGs in Apoe^−/−Ndst1^f/fAlb-Cre⁺ mice, which was associated with increased LPL activity in white adipose tissue in the fed state. Finally, clinical data confirmed that ASO-mediated lowering of APOC-III via volanesorsen can reduce plasma TG levels independent of the APOE isoform genotype. Our data indicate that apoE determines the metabolic impact of apoC-III as we establish that apoE is essential to mediate inhibition of TRL clearance by apoC-III and that, in the absence of functional apoE, apoC-III inhibits tissue LPL activity.

Apolipoprotein profiling as a personalized approach to the diagnosis and treatment of dyslipidaemia

An elevated low-density lipoprotein cholesterol concentration is a classical risk factor for cardiovascular disease. This has led to pharmacotherapy in patients with atherosclerotic heart disease or high heart disease risk with statins to reduce serum low-density lipoprotein cholesterol. Even in patients in whom the target levels of low-density lipoprotein cholesterol are reached, there remains a significant residual cardiovascular risk; this is due, in part, to a focus on low-density lipoprotein cholesterol alone and neglect of other important aspects of lipoprotein metabolism. A more refined lipoprotein analysis will provide additional information on the accumulation of very low-density lipoproteins, intermediate density lipoproteins, chylomicrons, chylomicron-remnants and Lp(a) concentrations. Instead of measuring the cholesterol and triglyceride content of the lipoproteins, measurement of their apolipoproteins (apos) is more informative. Apos are either specific for a particular lipoprotein or for a group of lipoproteins. In particular measurement of apos in atherogenic particles is more biologically meaningful than the measurement of the cholesterol concentration contained in these particles. Applying apo profiling will not only improve characterization of the lipoprotein abnormality, but will also improve definition of therapeutic targets. Apo profiling aligns with the concept of precision medicine by which an individual patient is not treated as 'average' patient by the average (dose of) therapy. This concept of precision medicine fits the unmet clinical need for stratified cardiovascular medicine. The requirements for clinical application of proteomics, including apo profiling, can now be met using robust mass spectrometry technology which offers desirable analytical performance and standardization.

The Forgotten Lipids: Triglycerides, Remnant Cholesterol, and Atherosclerotic Cardiovascular Disease Risk

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of death worldwide. Low-density lipoprotein cholesterol (LDL-C) is a well-established mediator of atherosclerosis and a key target for intervention for the primary and secondary prevention of ASCVD. However, despite substantial reduction in LDL-C, patients continue to have recurrent ASCVD events. Hypertriglyceridemia may be an important contributor of this residual risk. Observational and genetic epidemiological data strongly support a causal role of triglycerides (TGs) and the cholesterol content within triglyceride-rich lipoproteins (TGRLs) and/or remnant cholesterol (RC) in the development of ASCVD. TGRLs are composed of hepatically derived very low-density lipoprotein and intestinally derived chylomicrons. RC is the cholesterol content of all TGRLs and plasma TGs serve as a surrogate measure of TGRLs and RC. Although lifestyle modification remains the cornerstone for management of hypertriglyceridemia, many novel drugs are in development and have shown impressive efficacy in lowering TG levels. Several ongoing, randomized controlled trials are underway to examine the impact of these novel agents on ASCVD outcomes. In this comprehensive review, we provide an overview of the biology, epidemiology, and genetics of TGs and ASCVD; we discuss current and novel TG-lowering therapies under development.

Increased inflammation, endoplasmic reticulum stress and oxidative stress in endothelial and macrophage cells exacerbate atherosclerosis in ApoCIII transgenic mice

Background

Overexpression of apolipoprotein CIII (ApoCIII) leads to hypertriglyceridemia (HTG) which promotes atherosclerosis development. However, it remains unclear whether ApoCIII affects the atherosclerosis alone by promoting the inflammation and endoplasmic reticulum (ER) stress, or in combination with HTG.

Methods

Transgenic (ApoCIIItg) mouse models were used to investigate the atherogenic role of ApoCIII. Since endothelial cells and macrophages play crucial roles in atherosclerosis, we examined whether triglyceride-rich lipoproteins (TRLs), the major lipoproteins, in plasma of ApoCIIItg mice affect inflammation and ER stress levels in these cells. To further investigate the role of ApoCIII and triglyceride, we incubated HUVECs cells and peritoneal macrophages with TRLs with or without ApoCIII.

Results

Increased inflammation and ER stress were found in the aorta of ApoCIIItg mice. TRLs increased ER stress and oxidative stress in HUVECs and macrophages in a dose dependent. Moreover, TRLs together with ApoCIII could induce a higher inflammation level than TRLs alone in these cells.

Conclusions

Both TRLs and ApoCIII contribute to the progression of atherosclerosis, and the modulation of TRLs and ApoCIII may represent a novel therapeutic approach against HTG induced atherosclerosis.

Reduction in Secretion of Very Low Density Lipoprotein-Triacylglycerol by a Matrix Metalloproteinase Inhibitor in a Rat Model of Diet-Induced Hypertriglyceridemia

Matrix metalloproteinase inhibitors (MMPIs) reduced serum triacylglycerol (TAG) levels in streptozotocin-induced diabetic rats and Zucker fa/fa rats in our previous study. However, the mechanisms underlying TAG reduction by MMPIs remain unclear. The present study aimed to elucidate the mechanism by which F81-1144b, an MMPI, lowers serum TAG levels in an animal model of high-sucrose diet (HSD)-induced hypertriglyceridemia. F81-1144b was repeatedly administered to rats fed HSD, and its effects were evaluated on TAG levels in serum and the liver, very low density lipoprotein (VLDL) secretion, de novo fatty acid (FA) synthesis in the liver, and the expression of genes regulating the metabolism of FA, TAG, and VLDL in the liver and serum. F81-1144b lowered TAG levels in serum and the liver, VLDL-TAG secretion, de novo FA synthesis in the liver, and serum levels of insulin and glucose. F81-1144b suppressed the expression of genes related to the de novo synthesis of FA and TAG, key proteins (lipin 1 and apolipoprotein CIII) responsible for VLDL metabolism, and sterol regulatory element-binding protein-1c and carbohydrate response element-binding protein. F81-1144b little affected the expression of genes related directly to the degradation of TAG or FA, but it upregulated that of gene for uncoupling protein 2 in the liver. These results suggest that MMPIs are a novel type of therapeutic agent for the treatment of hypertriglyceridemia, because the metabolic effects of F81-1144b expected from changes in the expression of genes regulating lipid metabolism would alter metabolism differently from those induced by fibrates, niacin, or n-3 FAs.

Apolipoprotein C-III in triglyceride-rich lipoprotein metabolism

PURPOSE OF REVIEW

Apolipoprotein (apo) C-III is a key player in triglyceride-rich lipoprotein metabolism and strongly associated with elevated plasma triglyceride levels. Several new studies added important insights on apoC-III and its physiological function confirming its promise as a valid therapeutic target.

RECENT FINDINGS

APOC3 is expressed in liver and intestine and regulates triglyceride-rich lipoprotein (TRL) catabolism and anabolism. The transcriptional regulation in both organs requires different regulatory elements. Clinical and preclinical studies established that apoC-III raises plasma triglyceride levels predominantly by inhibiting hepatic TRL clearance. Mechanistic insights into missense variants indicate accelerated renal clearance of apoC-III variants resulting in enhanced TRL catabolism. In contrast, an APOC3 gain-of-function variant enhances de novo lipogenesis and hepatic TRL production. Multiple studies confirmed the correlation between increased apoC-III levels and cardiovascular disease. This has opened up new therapeutic avenues allowing targeting of specific apoC-III properties in triglyceride metabolism.

SUMMARY

Novel in vivo models and APOC3 missense variants revealed unique mechanisms by which apoC-III inhibits TRL catabolism. Clinical trials with Volanesorsen, an APOC3 antisense oligonucleotide, report very promising lipid-lowering outcomes. However, future studies will need to address if acute apoC-III lowering will have the same clinical benefits as a life-long reduction.

High-Density Lipoprotein Subspecies Defined by Apolipoprotein C-III and Subclinical Atherosclerosis Measures: MESA (The Multi-Ethnic Study of Atherosclerosis)

Background

Apolipoprotein C‐III (apoC‐III), a small proinflammatory protein present on 6% to 7% of high‐density lipoprotein (HDL) particles, defines a subspecies of HDL adversely associated with coronary heart disease in primarily white cohorts. In a multi‐ethnic population free of clinical cardiovascular disease, we evaluated the relationship between apoC‐III–defined HDL subspecies and subclinical markers of atherosclerotic pathology.

Methods and Results

We investigated cross‐sectional associations between apolipoprotein A‐I concentrations of apoC‐III–defined HDL subspecies, measured via ELISA and imaging measures of subclinical atherosclerosis, among 4659 participants in the MESA (The Multi‐Ethnic Study of Atherosclerosis) at baseline (2000–2002). HDL particles containing and lacking apoC‐III were divergently associated with coronary artery calcification in women (P‐heterogeneity=0.002) but not in men (P‐heterogeneity=0.31) and with carotid plaque score (P‐heterogeneity=0.02) and intima‐media thickness (P‐heterogeneity=0.06) in the overall study population. HDL lacking apoC‐III was inversely associated with all outcome measures (coronary artery calcification, women: odds ratio per SD=0.81 [95% confidence interval [CI], 0.73–0.90]; carotid plaque, overall: odds ratio per SD=0.92 [95% CI, 0.84–1.00]; intima‐media thickness, overall: mean difference per SD=−14.0 µm [95% CI, −21.1 to −6.7 μm]), whereas HDL containing apoC‐III was positively associated (coronary artery calcification, women: odds ratio=1.10 [95% CI, 0.99–1.22]; plaque, overall: odds ratio=1.10 [95% CI, 1.01–1.19]) or unassociated. Neither total HDL nor HDL subspecies was associated with changes in subclinical atherosclerosis measures up to 10 years later.

Conclusions

The presence of apoC‐III defined a subspecies of HDL not inversely associated with baseline measures of subclinical atherosclerosis, supporting a role of apoC‐III in the pathophysiology of cardiovascular disease.

New medications targeting triglyceride-rich lipoproteins: Can inhibition of ANGPTL3 or apoC-III reduce the residual cardiovascular risk?

Remarkably good results have been achieved in the treatment of atherosclerotic cardiovascular diseases (CVD) by using statin, ezetimibe, antihypertensive, antithrombotic, and PCSK9 inhibitor therapies and their proper combinations. However, despite this success, the remaining CVD risk is still high. To target this residual risk and to treat patients who are statin-intolerant or have an exceptionally high CVD risk for instance due to familial hypercholesterolemia (FH), new therapies are intensively sought. One pathway of drug development is targeting the circulating triglyceride-rich lipoproteins (TRL) and their lipolytic remnants, which, according to the current view, confer a major CVD risk. Angiopoietin-like protein 3 (ANGPTL3) and apolipoprotein C-III (apoC-III) are at present the central molecular targets for therapies designed to reduce TRL, and there are new drugs emerging that suppress their expression or inhibit the function of these two key proteins. The medications targeting these components are biological, either human monoclonal antibodies or antisense oligonucleotides. In this article, we briefly review the mechanisms of action of ANGPTL3 and apoC-III, the reasons why they have been considered promising targets of novel therapies for CVD, as well as the current status and the most important results of their clinical trials.

Key differences between apoC-III regulation and expression in intestine and liver

ApoC-III is a critical cardiovascular risk factor, and humans expressing null mutations in apoC-III are robustly protected from cardiovascular disease. Because of its critical role in elevating plasma lipids and CVD risk, hepatic apoC-III regulation has been studied at length. Considerably less is known about the factors that regulate intestinal apoC-III. In this work, we use primary murine enteroids, Caco-2 cells, and dietary studies in wild-type mice to show that intestinal apoC-III expression does not change in response to fatty acids, glucose, or insulin administration, in contrast to hepatic apoC-III. Intestinal apoC-III is not sensitive to changes in FoxO1 expression (which is itself very low in the intestine, as is FoxO1 target IGFBP-1), nor is intestinal apoC-III responsive to western diet, a significant contrast to hepatic apoC-III stimulation during western diet. These data strongly suggest that intestinal apoC-III is not a FoxO1 target and support the idea that apoC-III is not regulated coordinately with hepatic apoC-III, and establishes another key aspect of apoC-III that is unique in the intestine from the liver.

Apolipoprotein C-III and High-Density Lipoprotein Subspecies Defined by Apolipoprotein C-III in Relation to Diabetes Risk

Apolipoprotein C-III (apoC-III) is a potentially novel biomarker that may play an important role in the pathogenesis of diabetes, particularly when present on the surface of high-density lipoprotein (HDL). In a case-cohort study carried out among 434 incident diabetes cases occurring before 2007 and 3,101 noncases in the Danish Diet, Cancer, and Health Study, we examined associations of baseline (1993-1997) plasma concentrations of apoC-III and subspecies of HDL defined by the presence or absence of apoC-III with risk of diabetes using Cox regression. ApoC-III was strongly associated with risk of diabetes (for top quintile vs. bottom quintile, hazard ratio (HR) = 3.43, 95% confidence interval (CI): 1.75, 6.70; P-trend < 0.001). The cholesterol concentration of HDL (HDL cholesterol (HDL-C)) without apoC-III was inversely associated with risk of diabetes (HR = 0.48, 95% CI: 0.27, 0.85; P-trend = 0.002), more so than total HDL-C (HR = 0.60, 95% CI: 0.35, 1.03; P-trend = 0.04), whereas HDL-C with apoC-III was not associated (HR = 1.05, 95% CI: 0.50, 2.21; P-trend = 0.44) (for HDL-C with apoC-III vs. HDL-C without apoC-III, P-heterogeneity = 0.002). ApoC-III itself is a strong risk marker for diabetes, and its presence on HDL may impair the antidiabetogenic properties of HDL. ApoC-III has potential to be a therapeutic target for the prevention of diabetes.

The apolipoprotein C-III (Gln38Lys) variant associated with human hypertriglyceridemia is a gain-of-function mutation

Recent cell culture and animal studies have suggested that expression of human apo C-III in the liver has a profound impact on the triacylglycerol (TAG)-rich VLDL₁ production under lipid-rich conditions. The apoC-III Gln38Lys variant was identified in subjects of Mexican origin with moderate hypertriglyceridemia. We postulated that Gln38Lys (C3^QK), being a gain-of-function mutation, promotes hepatic VLDL₁ assembly/secretion. To test this hypothesis, we expressed C3^QK in McA-RH7777 cells and apoc3-null mice to contrast its effect with WT apoC-III (C3^WT). In both model systems, C3^QK expression increased the secretion of VLDL₁-TAG (by 230%) under lipid-rich conditions. Metabolic labeling experiments with C3^QK cells showed an increase in de novo lipogenesis (DNL). Fasting plasma concentration of TAG, cholesterol, cholesteryl ester, and FA were increased in C3^QK mice as compared with C3^WT mice. Liver of C3^QK mice also displayed an increase in DNL and expression of lipogenic genes as compared with that in C3^WT mice. These results suggest that C3^QK variant is a gain-of-function mutation that can stimulate VLDL₁ production, through enhanced DNL.

Targeting ApoC-III to Reduce Coronary Disease Risk

Triglyceride-rich lipoproteins (TRLs) are causal contributors to the risk of developing coronary artery disease (CAD). Apolipoprotein C-III (apoC-III) is a component of TRLs that elevates plasma triglycerides (TGs) through delaying the lipolysis of TGs and the catabolism of TRL remnants. Recent human genetics approaches have shown that heterozygous loss-of-function mutations in APOC3, the gene encoding apoC-III, lower plasma TGs and protect from CAD. This observation has spawned new interest in therapeutic efforts to target apoC-III. Here, we briefly review both currently available as well as developing therapies for reducing apoC-III levels and function to lower TGs and cardiovascular risk. These therapies include existing options including statins, fibrates, thiazolidinediones, omega-3-fatty acids, and niacin, as well as an antisense oligonucleotide targeting APOC3 currently in clinical development. We review the mechanisms of action by which these drugs reduce apoC-III and the current understanding of how reduction in apoC-III may impact CAD risk.

A Novel Role for RARα Agonists as Apolipoprotein CIII Inhibitors Identified from High Throughput Screening

Elevated triglyceride (TG) levels are well-correlated with the risk for cardiovascular disease (CVD). Apolipoprotein CIII (ApoC-III) is a key regulator of plasma TG levels through regulation of lipolysis and lipid synthesis. To identify novel regulators of TG levels, we carried out a high throughput screen (HTS) using an ApoC-III homogenous time resolved fluorescence (HTRF) assay. We identified several retinoic acid receptor (RAR) agonists that reduced secreted ApoC-III levels in human hepatic cell lines. The RARα specific agonist AM580 inhibited secreted ApoC-III by >80% in Hep3B cells with an EC₅₀ ~2.9 nM. In high-fat diet induced fatty-liver mice, AM580 reduced ApoC-III levels in liver as well as in plasma (~60%). In addition, AM580 treatment effectively reduced body weight, hepatic and plasma TG, and total cholesterol (TC) levels. Mechanistically, AM580 suppresses ApoC-III synthesis by downregulation of HNF4α and upregulation of SHP1 expression. Collectively, these studies suggest that an RARα specific agonist may afford a new strategy for lipid-lowering and CVD risk reduction.

Non-alcoholic fatty liver disease--a chronic disease of the 21^st century

Non-alcoholic fatty liver disease (NAFLD) comprises a spectrum of metabolic states ranging from simple steatosis to inflammation with associated fibrosis to cirrhosis. Though accumulation of hepatic fat is not associated with a significant increase in mortality rates, hepatic inflammation is, as this augments the risk of terminal liver disease, i.e., cirrhosis, hepatic decompensation (liver failure) and/or hepatocellular carcinoma. Disease progression is usually slow, over a decade or more and, for the most part, remains asymptomatic. Recent estimates suggest that the global prevalence of NAFLD is high, about one in four. In most cases, NAFLD overlaps with overweight, obesity, cardiovascular disease and the metabolic syndrome with numerous contributing parameters including a dysregulation of adipose tissue, insulin resistance, type 2 diabetes, changes in the gut microbiome, neuronal and hormonal dysregulation and metabolic stress. NAFLD is diagnosed incidentally, despite its high prevalence. Non-invasive imaging techniques have emerged, making it possible to determine degree of steatosis as well asfibrosis. Despite this, the benefit of routine diagnostics remains uncertain. A better understanding of the (molecular) pathogenesis of NAFLD is needed combined with long-term studies where benefits of treatment can be assessed to determine cost-benefit ratios. This review summarizes the current state of knowledge and possible areas of treatment.

Aromatic residues in the C terminus of apolipoprotein C-III mediate lipid binding and LPL inhibition

Plasma apoC-III levels correlate with triglyceride (TG) levels and are a strong predictor of CVD outcomes. ApoC-III elevates TG in part by inhibiting LPL. ApoC-III likely inhibits LPL by competing for lipid binding. To probe this, we used oil-drop tensiometry to characterize binding of six apoC-III variants to lipid/water interfaces. This technique monitors the dependence of lipid binding on surface pressure, which increases during TG hydrolysis by LPL. ApoC-III adsorption increased surface pressure by upward of 18 mN/m at phospholipid/TG/water interfaces. ApoC-III was retained to high pressures at these interfaces, desorbing at 21-25 mN/m. Point mutants, which substituted alanine for aromatic residues, impaired the lipid binding of apoC-III. Adsorption and retention pressures decreased by 1-6 mN/m in point mutants, with the magnitude determined by the location of alanine substitutions. Trp42 was most critical to mediating lipid binding. These results strongly correlate with our previous results, linking apoC-III point mutants to increased LPL binding and activity at lipid surfaces. We propose that aromatic residues in the C-terminal half of apoC-III mediate binding to TG-rich lipoproteins. Increased apoC-III expression in the hypertriglyceridemic state allows apoC-III to accumulate on lipoproteins and inhibit LPL by preventing binding and/or access to substrate.

APOC3 Protein Is Not a Predisposing Factor for Fat-induced Nonalcoholic Fatty Liver Disease in Mice

Nonalcoholic fatty liver disease (NAFLD), characterized by excessive fat accumulation in liver, is prevalent in obesity. Genetic factors that link obesity to NAFLD remain obscure. Apolipoprotein C3 (APOC3) is a lipid-binding protein with a pivotal role in triglyceride metabolism. Humans with APOC3 gain-of-function mutations and mice with APOC3 overproduction are associated with hypertriglyceridemia. Nonetheless, it remains controversial whether APOC3 is culpable for diet-induced NAFLD. To address this fundamental issue, we fed APOC3-transgenic and wild-type littermates a high fructose diet or high fat diet, followed by determination of the effect of APOC3 on hepatic lipid metabolism and inflammation and the progression of NAFLD. To gain mechanistic insight into NAFLD, we determined the impact of APOC3 on hepatic triglyceride synthesis and secretion versus fatty acid oxidation. APOC3-transgenic mice were hypertriglyceridemic, culminating in marked elevation of triglycerides, cholesterols, and non-esterified fatty acids in plasma. Despite the prevailing hypertriglyceridemia, APOC3-transgenic mice, relative to wild-type littermates, had similar weight gain and hepatic lipid content without alterations in hepatic expression of key genes involved in triglyceride synthesis and secretion and fatty acid oxidation. APOC3-transgenic and wild-type mice had similar Kupffer cell content without alterations in hepatic expression of pro- and anti-inflammatory cytokines. APOC3 neither exacerbated diet-induced adiposity nor aggravated the degree of steatosis in high fructose or high fat-fed APOC3-transgenic mice. These effects ensued independently of weight gain even after 10-month high fat feeding. We concluded that APOC3, whose dysregulation is liable for hypertriglyceridemia, is not a predisposing factor for linking overnutrition to NAFLD in obesity.

Targeting microsomal triglyceride transfer protein and lipoprotein assembly to treat homozygous familial hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) is a polygenic disease arising from defects in the clearance of plasma low-density lipoprotein (LDL), which results in extremely elevated plasma LDL cholesterol (LDL-C) and increased risk of atherosclerosis, coronary heart disease, and premature death. Conventional lipid-lowering therapies, such as statins and ezetimibe, are ineffective at lowering plasma cholesterol to safe levels in these patients. Other therapeutic options, such as LDL apheresis and liver transplantation, are inconvenient, costly, and not readily available. Recently, lomitapide was approved by the Federal Drug Administration as an adjunct therapy for the treatment of HoFH. Lomitapide inhibits microsomal triglyceride transfer protein (MTP), reduces lipoprotein assembly and secretion, and lowers plasma cholesterol levels by over 50%. Here, we explain the steps involved in lipoprotein assembly, summarize the role of MTP in lipoprotein assembly, explore the clinical and molecular basis of HoFH, and review pre-clinical studies and clinical trials with lomitapide and other MTP inhibitors for the treatment of HoFH. In addition, ongoing research and new approaches underway for better treatment modalities are discussed.

Association of Apolipoprotein C3 Genetic Polymorphisms with the Risk of Ischemic Stroke in the Northern Chinese Han Population

The apolipoprotein C3 (APOC3) gene, which is a member of the APOA1/C3/A4/A5 gene cluster, plays a crucial role in lipid metabolism. Dyslipidemia is an important risk factor for ischemic stroke. In the present study, we performed a hospital-based case-control study of 895 ischemic stroke patients and 883 control subjects to examine the effects of four APOC3 single nucleotide polymorphisms (SNPs) (rs2854116, rs2854117, rs4520 and rs5128) on the risk of ischemic stroke in a northern Chinese Han population. The SNaPshot Multiplex sequencing assay was used for SNP genotyping, and the potential association of genotype distributions and allele frequencies with ischemic stroke was analyzed statistically. Compared with the GG genotype, the CC+GC genotype of rs5128 was significantly associated with an increased risk in females (adjusted OR = 3.38, 95% CI = 1.82-6.28, P <0.01) after all of the risk factors were adjusted for with logistic regression analyses. A similar relationship was found between the rs4520 polymorphism and ischemic stroke risk in Han Chinese women. Under a recessive genetic model, the TT+TC genotypes of this variant increased ischemic stroke risk (adjusted OR = 2.05; 95% CI = 1.28-3.29; P <0.01). Haplotype analysis revealed that in males, the T-C-T-C haplotype of rs2854116-rs2854117-rs4520-rs5128 was significantly more frequent in the ischemic stroke group than in the control group (OR = 1.49, 95% CI = 1.18-1.87, P<0.01). The results of our study indicate that the APOC3 polymorphisms contribute to ischemic stroke susceptibility in females in the northern Chinese Han population.