Apolipoprotein C3: form begets function

Proteomic Profiling of Age-Related Proteins Following Extracorporeal Apheresis

Lipoprotein apheresis (LA) is often the last option to adequately reduce lipoproteins in patients with familial hypercholesterolemia and lipoprotein (a) hyperlipidemia. Characterized by mild side effects, it is now the most effective method of preventing major cardiovascular events (CVEs). This benefit is due not only to the lowering of lipoprotein levels, but probably also to many other pleiotropic effects that have been extensively described in the literature. These include the reduction of inflammatory signaling substances, fibrinogen, plasminogen or components of the oxidative stress response. Here, we performed a proteomic analysis of 12 patients treated with therapeutic apheresis using two different pore size filters to quantify the effect on age-related plasma proteins. This study showed that important proteins such as α-2-macroglobulin, apolipoprotein C-III, complement C1s subcomponent, C4b-binding protein alpha chain, CD5 antigen-like and pregnancy zone protein, whose role in numerous aging processes has been well described, were significantly reduced by apheresis treatment. We conclude that therapeutic apheresis may be a promising approach to reduce these age-related proteins and that these treatments may become an essential part of managing cardiovascular risk in an aging population.

Apolipoprotein CIII correlates with lipoproteins in the fed state and is not regulated by leptin administration in states of hypoleptinemia induced by acute or chronic energy deficiency: Results from two randomised controlled trials

BACKGROUND

Medications targeting the leptin and Apolipoprotein CIII (APOC3) pathways are currently under development for the treatment of hypertriglyceridaemia. Given that both pathways are implicated in triglyceride regulation, it is unknown whether they function independently or interact under physiological conditions and under acute or long-term energy deficiency.

METHODS

APOC3 levels and their association with circulating lipids and lipoproteins were evaluated in the context of two randomised controlled studies. In Study-1, 15 healthy individuals were examined under three distinct conditions, each lasting 72 h: isocaloric feeding, fasting with placebo administration and fasting with leptin administered at replacement doses. In Study-2, 20 females with hypoleptinemia due to relative energy deficiency in sport (REDs) for a minimum of 6 months were treated with either leptin or a placebo for 36 weeks.

RESULTS

In Study-1, APOC3 levels remained stable across all arms and were unaffected by leptin administration. In the fed state, APOC3 levels presented positive correlations with various VLDL, IDL, LDL and HDL sizes, and free fatty acids (FFA), most of which were not replicated in fasting. During complete energy deprivation, APOC3 was correlated with HDL molecules, glutamine and FFA, whereas its levels were positively associated only with FFA under leptin treatment. In Study-2, APOC3 levels were lower in the leptin group, but this was not a leptin-dependent effect. A positive correlation between APOC3 levels and HDL was observed in the leptin group.

CONCLUSIONS

These results contribute towards our better understanding of the intricate nature of lipid regulation under energy deficiency, suggesting that medications targeting the leptin and APOC3 pathways act through different metabolic pathways and thus may have independent effects from each other in regulating triglycerides.

Remnant cholesterol concentrations best explain the cardiovascular benefit of APOC3 genetic inhibition: a drug target Mendelian randomization study

Aims

Apolipoprotein C-III (APOC3) inhibitors are approved for hypertriglyceridaemia. Genetic evidence suggests that APOC3 inhibition may also prevent coronary artery disease (CAD), but mechanisms remain unclear.

Methods and results

To clarify how APOC3 inhibition could prevent CAD, we performed two-step cis-Mendelian randomization using genetic variants in the APOC3 gene region associated with plasma levels of APOC3. For comparison, we investigated proprotein convertase subtilisin/kexin type 9 (PCSK9). Potential mediators included apolipoprotein B, triglycerides, LDL-cholesterol, and remnant cholesterol measured by nuclear magnetic resonance spectroscopy in mostly fasting samples from Karjalainen et al., and in non-fasting samples from the UK Biobank. CAD data were from CARDIoGRAMplusC4D. APOC3 associations with apolipoprotein B and remnant cholesterol levels were two-fold larger in the study by Karjalainen et al. (55% fasted individuals) when compared with the UK Biobank study (non-fasted individuals). Genetically predicted lower APOC3 and PCSK9 levels were similarly associated with reduced CAD risk (OR = 0.83, 95% CI = 0.75-0.92, P = 4.6e-04 and 0.76, 95% CI = 0.73-0.80, P = 1.6e-31, respectively). In the two-step cis-Mendelian randomization analysis, the association between genetically predicted APOC3 and CAD was attenuated to null when adjusting for apolipoprotein B, triglycerides, or remnant cholesterol. Multivariable Mendelian randomization using genome-wide variants showed that remnant cholesterol, not triglycerides, was conditionally associated with CAD risk.

Conclusion

Remnant cholesterol best explains the mechanism through which APOC3 inhibition could prevent CAD. APOC3 inhibition may influence fasting remnant cholesterol to a greater extent than non-fasting remnant cholesterol. People with high levels of remnant cholesterol could benefit from APOC3 inhibition.

Apolipoprotein C3 and risk of cardiovascular events and death in patients on optimized statin treatment after recent acute coronary syndrome

AIMS

Apolipoprotein (Apo) C3 has been associated with incident coronary heart disease and major adverse cardiovascular events (MACE). Whether ApoC3 levels predict risk in patients with acute coronary syndrome (ACS) on optimized statin treatment is unknown.

METHODS

ApoC3 was measured by mass spectrometry at baseline (n=11,956) and after 4 months' treatment (M4; n=11 176) with alirocumab or placebo in the ODYSSEY OUTCOMES trial. Patients with fasting triglycerides >400 mg/dL were excluded. The association of baseline ApoC3 with risk of MACE or death was assessed in post hoc adjusted Cox regression models and spline analyses adjusted for treatment and ApoB. In adjusted models in the alirocumab group we determined association of ApoC3 change from baseline to M4 with subsequent risk of MACE and death.

RESULTS

Median (Q1, Q3) baseline ApoC3 concentration was 85 (65, 113) mg/L. With adjustment for ApoB, baseline ApoC3 showed no clinically meaningful relationship to risk of MACE or death in spline analyses and no association with MACE (P=0.89) or death (P=0.70) in Cox regression analyses. Alirocumab reduced ApoC3 modestly by median -10 (-27, -5) mg/L (P<0.0001) and reduced MACE (10.1% vs 12.1%; P=0.0006) and death (3.5% vs 4.2%; P=0.045) versus placebo. However, the change in ApoC3 on alirocumab did not predict subsequent MACE or death.

CONCLUSION

In patients with recent ACS on optimized statins without severe hypertriglyceridemia, neither baseline ApoC3 (accounting for ApoB) nor ApoC3 change with alirocumab predicted MACE or death. It is uncertain whether targeted therapies producing larger reductions in ApoC3 from higher baseline levels will affect cardiovascular risk.

Current and Emerging Treatment Options for Hypertriglyceridemia: State-of-the-Art Review

Hypertriglyceridemia (HTG) is associated with a residual risk of atherosclerotic cardiovascular disease. Extremely elevated triglyceride (TG) concentrations, particularly due to familial chylomicronemia syndrome (FCS), pose a risk for acute pancreatitis. Standard therapies with statins, fibrates, omega-3 fatty acids, and niacin may be insufficient to reduce elevated TG levels and improve clinical outcomes in patients with HTG. Novel antisense oligonucleotides and small interfering ribonucleic acids target the key modulators of TG-rich lipoprotein catabolism. Among apolipoprotein C-III (apoC-III) inhibitors, olezarsen and plozasiran appear to be safer alternatives for volanesorsen regarding the risk of drug-induced thrombocytopenia in patients with FCS or severe HTG. After the failure of vupanorsen, a new angiopoietin-like protein 3 (ANGPTL3) inhibitor, zodasiran, demonstrated the potential to decrease TG levels in patients with moderate HTG. Meanwhile, the fibroblast growth factor 21 (FGF21) analog, pegozafermin, became another candidate for the treatment of severe HTG. This comprehensive review outlines pharmacological targets in TG-rich lipoprotein metabolism, discusses international guidelines, and summarizes the latest evidence from clinical trials to provide insight into the current and emerging treatment options for primary HTG.

Molecular Regulation and Therapeutic Targeting of VLDL Production in Cardiometabolic Disease

There exists a complex relationship between steatotic liver disease (SLD) and atherosclerotic cardiovascular disease (CVD). CVD is a leading cause of morbidity and mortality among individuals with SLD, particularly those with metabolic dysfunction-associated SLD (MASLD), a significant proportion of whom also exhibit features of insulin resistance. Recent evidence supports an expanded role of very low-density lipoprotein (VLDL) in the pathogenesis of CVD in patients, both with and without associated metabolic dysfunction. VLDL represents the major vehicle for exporting neutral lipid from hepatocytes, with each particle containing one molecule of apolipoproteinB100 (APOB100). VLDL production becomes dysregulated under conditions characteristic of MASLD including steatosis and insulin resistance. Insulin resistance not only affects VLDL production but also mediates the pathogenesis of atherosclerotic CVD. VLDL assembly and secretion therefore represents an important pathway in the setting of cardiometabolic disease and offers several candidates for therapeutic targeting, particularly in metabolically complex patients with MASLD at increased risk of atherosclerotic CVD. Here we review the clinical significance as well as the translational and therapeutic potential of key regulatory steps impacting VLDL initiation, maturation, secretion, catabolism, and clearance.

Olezarsen, a liver-directed APOC3 ASO therapy for hypertriglyceridemia

INTRODUCTION

Apolipoprotein (apo)C-III, a key regulator of plasma triglyceride (TG) levels, is a prime candidate for the treatment of hypertriglyceridemia (HTG), prevention of acute pancreatitis, and reduction of future atherosclerotic cardiovascular disease (ASCVD) events.

AREAS COVERED

We discuss the role of apoC-III as a therapeutic target for HTG, describe the pharmacodynamics, pharmacokinetics, and metabolism of olezarsen, as well as report on the findings of recent clinical trials with this liver-directed APOC3 antisense oligonucleotide (ASO).

EXPERT OPINION

Olezarsen, a GalNac-conjugated ASO targeting apoC-III, can reduce TG levels by ~ 50% in patients with extreme HTG due to familial chylomicronemia syndrome, as well as in patients with moderate HTG. Attention is now focused on whether olezarsen reduces ASCVD risk in patients with moderate and severe HTG. While olezarsen does cause elevations in liver enzymes, these changes are not clinically meaningful, and are not associated with thrombocytopenia, an issue with its predecessor, volanesorsen. The need for 4-weekly administration puts olezarsen at a disadvantage to competing injectables. Results from the CORE, CORE2, and ESSENCE phase III clinical trials in patients with severe HTG, expected in the second half of 2025, will help determine the requirement for a larger cardiovascular outcomes trial.

A brief clinical genetics review: stepwise diagnostic processes of a monogenic disorder-hypertriglyceridemia

The completion of the Human Genome Project and tremendous advances in automated high-throughput genetic analysis technologies have enabled explosive progress in the field of genetics, which resulted in countless discoveries of novel genes and pathways. Many phenotype- or disease-associated single nucleotide polymorphisms (SNPs) with a high statistical significance have been identified through numerous genome-wide association studies (GWAS), and various polygenic risk scoring (PRS) schemes have been proposed to identify individuals with a high risk for a certain trait or disorder. Meanwhile, medical education in genetics has lagged far behind, leaving many physicians and healthcare providers unprepared in the genomic era. Thus, there is an urgent need to educate physicians and healthcare providers with basic knowledge and skills in genetics. To facilitate this, some basic terminologies and concepts are discussed in this review. In addition, some important considerations in delineating and incorporating clinical genetic testing in the diagnosis and management of a monogenic disorder are illustrated in a stepwise fashion. Furthermore, the effects of disease-associated SNPs represented by a PRS scheme clearly demonstrated that even the phenotypes of a monogenic disorder due to the same pathogenic variant in family members are modulated by the polygenic background. In human genetics, despite these explosive advancements, we are still far from clearly deciphering the interplay of gene variants to effect unique characteristics in an individual. In addition, sophisticated genome or gene directed therapies are being investigated for numerous disorders. Therefore, evolution in the field of genetics is likely to continue into the foreseeable future. In the meantime, much emphasis should be placed on educating physicians and healthcare professionals to be well-versed and skillful in the clinical use of genetics so that they can fully embrace the new era of precision medicine.

Inhibitors of apolipoprotein C3, triglyceride levels, and risk of pancreatitis: a systematic review and meta-analysis

In recent years, novel apoC3 inhibitor therapies for the treatment of hypertriglyceridemia have been developed and assessed through phase II and III clinical trials. The objective of this study was to perform an updated meta-analysis on the impact of new apoC3 inhibitor drugs on triglyceride and apoC3 levels, as well as on the incidence of pancreatitis. We conducted a meta-analysis of randomized, placebo-controlled studies assessing the effects of apoC3 inhibitors therapy (antisense oligonucleotides and small interfering RNA) on triglyceride levels, apoC3 levels, and the occurrence of acute pancreatitis. This meta-analysis was performed according to PRISMA guidelines. The random-effects model was performed. Nine randomized clinical trials (n = 717 patients) were considered eligible for this systematic review. ApoC3 inhibitor drugs were consistently associated with decreased triglyceride levels (MD -57.0%; 95% CI -61.9 to -52.1, I2 82%) and lowered apoC3 values (MD -76; 95% CI -80.1 to -71.8, I2 77%) when compared to placebo. Furthermore, the use of apoC3 inhibitor drugs demonstrated a reduction in the risk of acute pancreatitis (OR 0.11; 95% CI 0.04 to 0.27, I2 0%). The present updated meta-analysis of randomized clinical trials demonstrated that the utilization of apoC3 inhibitors in patients with hypertriglyceridemia correlated with reduced apoC3 and triglyceride levels, along with a decreased risk of acute pancreatitis compared to the placebo.

Decreased Serum Apolipoprotein CIII in the Acute Phase of Kawasaki Disease

Plasma exchange is an effective treatment for Kawasaki disease (KD), suggesting that plasma from patients with KD bears its causative agents. The aim of this study was to use mass spectrometry to identify candidate agents in patient sera. Serum samples were obtained from 17 KD patients. In six patients, samples were collected in each of three phases: the acute phase prior to acetylsalicylic acid (ASA) and intravenous immunoglobulin administration (Phase A1), the remission phase with ASA (Phase A2), and the remission phase without any medication (Phase A3). Sera from the remaining 11 patients were collected during Phases A1 and A2. The study also included two age- and gender-matched control groups, one with eight afebrile children and one with eight febrile children diagnosed with infectious disease. Patients in Phase A1 and febrile controls did not differ in body temperature, white blood cell counts, or C-reactive protein levels. Mass spectrometry analysis revealed that the intensity levels of m/z 9416, identified as apolipoprotein CIII (Apo CIII), were lower in Phase A1 samples compared with samples from patients in Phases A2 and A3, and from febrile controls (all comparisons, p < 0.01). Serum Apo CIII levels were also lower in Phase A1 samples compared with samples from Phase A2 patients and afebrile controls (both p < 0.01), but samples from patients in Phase A2 did not differ significantly from those of the afebrile controls (p = 0.55). This study demonstrated that serum Apo CIII level was decreased in the acute phase of KD.

APOC3 siRNA and ASO therapy for dyslipidemia

PURPOSE OF REVIEW

The aim of this review is to present the clinical indications of apolipoprotein C-III (apoC3) inhibition in the therapeutic arsenal for the treatment of lipid disorders and associated risks and to compare the most advanced modalities of apoC3 inhibition currently available or in development, specifically APOC3 antisense oligonucleotides (ASO) and small interfering RNA (siRNA).

RECENT FINDINGS

ApoC3 inhibition significantly decreases triglyceride levels by mechanisms coupling both lipoprotein lipase (LPL) upregulation and LPL-independent mechanisms. The main apoC3 inhibitors in advanced clinical development are the GalNAc-ASO olezarsen and the GalNAc-siRNA plozasiran. Clinical studies conducted with volanesorsen, the olezarsen precursor, showed a favorable effect on hepatic steatosis (nonalcoholic fatty liver disease, NAFLD). Olezarsen does not appear to be associated with the main side effects attributed to volanesorsen including thrombocytopenia. Plozasiran is in advanced clinical development and requires subcutaneous injection every 3 months and present to-date an efficacy and safety profile comparable to that of the monthly ASO.

SUMMARY

Inhibition of apoC3 is effective across all the spectrum of hypertriglyceridemia, might have a favorable effect on hepatic steatosis (NAFLD) and the effect of apoC3 inhibition on cardiovascular risk is not limited to its effect on plasma triglycerides. APOC3 GalNAc-conjugated ASO and siRNA are both effective in decreasing plasma apoC3 and triglyceride levels.

High-Density Lipoprotein Is Located Alongside Insulin in the Islets of Langerhans of Normal and Rodent Models of Diabetes

Recent studies have implicated pre-beta and beta lipoproteins (VLDL and LDL) in the etiopathogenesis of complications of diabetes mellitus (DM). In contrast, alpha lipoprotein (HDL) is protective of the beta cells of the pancreas. This study examined the distribution of HDL in the islets of Langerhans of murine models of type 1 diabetic rats (streptozotocin (STZ)-induced DM in Wistar rats) and type 2 models of DM rats (Goto-Kakizaki (GK), non-diabetic Zucker lean (ZL), and Zucker diabetic and fatty (ZDF)). The extent by which HDL co-localizes with insulin or glucagon in the islets of the pancreas was also investigated. Pancreatic tissues of Wistar non-diabetic, diabetic Wistar, GK, ZL, and ZDF rats were processed for immunohistochemistry. Pancreatic samples of GK rats fed with either a low-fat or a high-fat diet were prepared for transmission immune-electron microscopy (TIEM) to establish the cytoplasmic localization of HDL in islet cells. HDL was detected in the core and periphery of pancreatic islets of Wistar non-diabetic and diabetic, GK, ZL, and ZDF rats. The average total of islet cells immune positive for HDL was markedly (<0.05) reduced in GK and ZDF rats in comparison to Wistar controls. The number of islet cells containing HDL was also remarkably (p < 0.05) reduced in Wistar diabetic rats and GK models fed on high-fat food. The co-localization study using immunofluorescence and TIEM techniques showed that HDL is detected alongside insulin within the secretory granules of β-cells. HDL did not co-localize with glucagon. This observation implies that HDL may contribute to the metabolism of insulin.