Familial combined hypolipidemia: angiopoietin-like protein-3 deficiency

Homozygous Familial Hypercholesterolemia Treatment: New Developments

PURPOSE OF REVIEW

Homozygous familial hypercholesterolaemia (HoFH) is characterized by marked elevation of low-density lipoprotein cholesterol (LDLC) and premature atherosclerotic cardiovascular disease. This is a review of novel pharmacological therapies to lower LDLC in patients with HoFH.

RECENT FINDINGS

Novel therapies can be broadly divided by whether their efficacy is dependent or independent of residual low-density lipoprotein receptor (LDLR) function. Novel LDLR dependent therapies that reduce proprotein subtilisin kexin type 9 levels include monoclonal antibodies (alirocumab and evolocumab) and a small inhibitory RNA (inclisiran). LDLC reductions are highly variable and depend on residual LDLR function. Microsomal triglyceride inhibitors (lomitapide) and therapies that reduce angiopoietin like factor 3 (evinacumab and zodasiran) both reduce LDLC by approximately 50%, irrespective of residual LDLR function. Most patients with HoFH require multiple therapies to achieve LDLC targets. Better LDLC control with LDLR independent therapies is likely to improve the outlook for patients with HoFH while at the same time reducing the need for other therapies such as apheresis or hepatic transplantation.

Inhibition of the ANGPTL3/8 Complex for the Prevention and Treatment of Atherosclerotic Cardiovascular Disease

PURPOSE OF REVIEW

Dyslipidemia is a casual risk factor for atherosclerotic cardiovascular disease (ASCVD). There is an unmet need for more effective treatments for patients with dyslipidemias. Angiopoietin-like protein 3 (ANGPTL3) and ANGPTL8 play key roles in triglyceride trafficking and energy balance in humans. We review the functional role of these ANGPTL proteins in the regulation of lipoprotein metabolism, and recent clinical trials targeting ANGPTL3 and ANGPTL3/8 with monoclonal antibody and/or nucleic acid therapies, including antisense oligonucleotides and small interfering RNA.

RECENT FINDINGS

Cumulative evidence supports the roles of ANGPTL3 and ANGPTL8 in lipid metabolism through inhibition of lipoprotein lipase and endothelial lipase activity. ANGPTL3 and ANGPTL3/8 inhibitors are effective in lowering plasma triglycerides and low-density lipoprotein (LDL)-cholesterol, with the possible advantage of raising high-density lipoprotein (HDL)-cholesterol with the inhibition of ANGPTL3/8. Therapeutic inhibition of ANGPTL3 and ANGPTL3/8 can lower plasma triglyceride and LDL-cholesterol levels possibly by lowering production and upregulating catabolism of triglyceride-rich lipoprotein and LDL particles. However, the effect of these novel agents on HDL metabolism remains unclear. The cardiovascular benefits of ANGPTL3 and ABGPTL3/8 inhibitors may also include improvement in vascular inflammation, but this requires further investigation.

Consensus document on diagnosis and management of familial hypercholesterolemia from the Italian Society for the Study of Atherosclerosis (SISA)

AIMS

Familial Hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism that causes an increased risk of premature atherosclerotic cardiovascular disease (ASCVD). Although early diagnosis and treatment of FH can significantly improve the cardiovascular prognosis, this disorder is underdiagnosed and undertreated. For these reasons the Italian Society for the Study of Atherosclerosis (SISA) assembled a Consensus Panel with the task to provide guidelines for FH diagnosis and treatment.

DATA SYNTHESIS

Our guidelines include: i) an overview of the genetic complexity of FH and the role of candidate genes involved in LDL metabolism; ii) the prevalence of FH in the population; iii) the clinical criteria adopted for the diagnosis of FH; iv) the screening for ASCVD and the role of cardiovascular imaging techniques; v) the role of molecular diagnosis in establishing the genetic bases of the disorder; vi) the current therapeutic options in both heterozygous and homozygous FH. Treatment strategies and targets are currently based on low-density lipoprotein cholesterol (LDL-C) levels, as the prognosis of FH largely depends on the magnitude of LDL-C reduction achieved by lipid-lowering therapies. Statins with or without ezetimibe are the mainstay of treatment. Addition of novel medications like PCSK9 inhibitors, ANGPTL3 inhibitors or lomitapide in homozygous FH results in a further reduction of LDL-C levels. LDL apheresis is indicated in FH patients with inadequate response to cholesterol-lowering therapies.

CONCLUSION

FH is a common, treatable genetic disorder and, although our understanding of this disease has improved, many challenges still remain with regard to its identification and management.

Lipid-lowering in diabetes: An update

Atherosclerotic cardiovascular disease (ASCVD) is accelerated in people with diabetes. Dyslipidemia, hyperglycemia, oxidative stress, and inflammation play a role via a variety of mechanisms operative in the artery wall. In addition, some unique features predispose people with type 1 diabetes to accelerated atherosclerosis. Various organizations have created guidelines that provide advice regarding screening, risk assessment, and roadmaps for treatment to prevent ASCVD in diabetes. Management of dyslipidemia, especially with statins, has proven to be of immense benefit in the prevention of clinical CVD. However, since many patients fail to attain the low levels of low-density lipoproteins (LDL) recommended in these guidelines, supplemental therapy, such as the addition of ezetimibe, bempedoic acid or PCSK9 inhibitors, is often required to reach LDL goals. As a result, the upfront use of combination therapies, particularly a statin plus ezetimibe, is a rational initial approach. The addition to statins of drugs that specifically lower triglyceride levels has not proven beneficial, although the addition of icosapent-ethyl has been shown to be of value, likely by mechanisms independent of triglyceride lowering. Newer treatments in development, including apoC-III and ANGPTL3 inhibitors, seem promising in further reducing apoB-containing lipoproteins.

ANGPTL3 Deficiency and Risk of Hepatic Steatosis

BACKGROUND

ANGPTL3 (angiopoietin-like 3) is a therapeutic target for reducing plasma levels of triglycerides and low-density lipoprotein cholesterol. A recent trial with vupanorsen, an antisense oligonucleotide targeting hepatic production of ANGPTL3, reported a dose-dependent increase in hepatic fat. It is unclear whether this adverse effect is due to an on-target effect of inhibiting hepatic ANGPTL3.

METHODS

We recruited participants with ANGPTL3 deficiency related to ANGPTL3 loss-of-function (LoF) mutations, along with wild-type (WT) participants from 2 previously characterized cohorts located in Campodimele, Italy, and St. Louis, MO. Magnetic resonance spectroscopy and magnetic resonance proton density fat fraction were performed to measure hepatic fat fraction and the distribution of extrahepatic fat. To estimate the causal relationship between ANGPTL3 and hepatic fat, we generated a genetic instrument of plasma ANGPTL3 levels as a surrogate for hepatic protein synthesis and performed Mendelian randomization analyses with hepatic fat in the UK Biobank study.

RESULTS

We recruited participants with complete (n=6) or partial (n=32) ANGPTL3 deficiency related to ANGPTL3 LoF mutations, as well as WT participants (n=92) without LoF mutations. Participants with ANGPTL3 deficiency exhibited significantly lower total cholesterol (complete deficiency, 78.5 mg/dL; partial deficiency, 172 mg/dL; WT, 188 mg/dL; P<0.05 for both deficiency groups compared with WT), along with plasma triglycerides (complete deficiency, 26 mg/dL; partial deficiency, 79 mg/dL; WT, 88 mg/dL; P<0.05 for both deficiency groups compared with WT) without any significant difference in hepatic fat (complete deficiency, 9.8%; partial deficiency, 10.1%; WT, 9.9%; P>0.05 for both deficiency groups compared with WT) or severity of hepatic steatosis as assessed by magnetic resonance imaging. In addition, ANGPTL3 deficiency did not alter the distribution of extrahepatic fat. Results from Mendelian randomization analyses in 36 703 participants from the UK Biobank demonstrated that genetically determined ANGPTL3 plasma protein levels were causally associated with low-density lipoprotein cholesterol (P=1.7×10-17) and triglycerides (P=3.2×10-18) but not with hepatic fat (P=0.22).

CONCLUSIONS

ANGPTL3 deficiency related to LoF mutations in ANGPTL3, as well as genetically determined reduction of plasma ANGPTL3 levels, is not associated with hepatic steatosis. Therapeutic approaches to inhibit ANGPTL3 production in hepatocytes are not necessarily expected to result in the increased risk for hepatic steatosis that was observed with vupanorsen.

Genetically determined deficiency of ANGPTL3 does not alter HDL ability to preserve endothelial homeostasis

Individuals with loss-of-function mutations in the ANGPTL3 gene express a rare lipid phenotype called Familial Combined Hypolipidemia (FHBL2). FHBL2 individuals show reduced plasma concentrations of total cholesterol and triglycerides as well as of lipoprotein particles, including HDL. This feature is particularly remarkable in homozygotes in whom ANGPTL3 in blood is completely absent. ANGPTL3 acts as a circulating inhibitor of LPL and EL and it is thought that EL hyperactivity is the cause of plasma HDL reduction in FHBL2. Nevertheless, the consequences of ANGTPL3 deficiency on HDL functionality have been poorly explored. In this report, HDL isolated from homozygous and heterozygous FHBL2 individuals were evaluated for their ability to preserve endothelial homeostasis as compared to control HDL. It was found that only the complete absence of ANGPTL3 alters HDL subclass distribution, as homozygous, but not heterozygous, carriers have reduced content of large and increased content of small HDL with no alterations in HDL2 and HDL3 size. The plasma content of preβ-HDL was reduced in carriers and showed a positive correlation with plasma ANGPTL3 levels. Changes in composition did not however alter the functionality of FHBL2 HDL, as particles isolated from carriers retained their capacity to promote NO production and to inhibit VCAM-1 expression in endothelial cells. Furthermore, no significant changes in circulating levels of soluble ICAM-1 and E-selectin were detected in carriers. These results indicate that changes in HDL composition associated with the partial or complete absence of ANGPTL3 did not alter some of the potentially anti-atherogenic functions of these lipoproteins.

How ANGPTL3 Inhibition Will Help Our Clinical Practice?

PURPOSE OF REVIEW

This review aims to summarize the most recently published literature highlighting the potential of pharmacological inhibition of ANGPTL3 in treating patients suffering from dyslipidemias. The rational for this strategy will be discussed considering evidence describing the role of ANGPTL3 in lipid metabolism and the consequences of its deficiency in humans.

RECENT FINDINGS

Recent trials have demonstrated the efficacy and safety of ANGPTL3 inhibition in treating homozygous familial hypercholesterolemia even in those patients carrying biallelic null/null variants, thus supporting the notion that the LDL-lowering effect of ANGPLT3 inhibition is LDLR-independent. The use of ANGPTL3 inhibition strategies has expanded its indications in hypertrygliceridemic patients with functional lipoprotein lipase activity. Contemporarily, the pharmacological research is exploring novel approaches to ANGPTL3 inhibition such as the use of a small interfering RNA targeting the ANGPTL3 transcript in the liver, a protein-based vaccine against ANGPTL3, and a CRISP-Cas-9 method for a liver-selective knock-out of ANGPTL3 gene. First, we will describe the molecular function of ANGPTL3 in lipoprotein metabolism. Then, we will revise the clinical characteristics of individuals carrying loss-of-function mutations of ANGPTL3, a rare condition known as familial hypobetalipoproteinemia type 2 (FHBL2) that represents a unique human model of ANGPTL3 deficiency. Finally, we will examine the lipid-lowering potential of pharmacological inhibition of ANGPTL3 based on the results of clinical trials employing Evinacumab, the first approved fully humanized monoclonal antibody against ANGPTL3. The future perspectives for ANGPTL3 inhibition will also be revised.

ANGPTL3 deficiency associates with the expansion of regulatory T cells with reduced lipid content

BACKGROUND AND AIMS

Angiopoietin-like 3 (ANGPTL3) regulates lipid and glucose metabolism. Loss-of-function mutations in its gene, leading to ANGPTL3 deficiency, cause in humans the familial combined hypolipidemia type 2 (FHBL2) phenotype, characterized by very low concentrations of circulating lipoproteins and reduced risk of atherosclerotic cardiovascular disease. Whether this condition is accompanied by immune dysfunctions is unknown. Regulatory T cells (Tregs) are CD4 T lymphocytes endowed with immune suppressive and atheroprotective functions and sensitive to metabolic signals. By investigating FHBL2, we explored the hypothesis that Tregs expand in response to extreme hypolipidemia, through a modulation of the Treg-intrinsic lipid metabolism.

METHODS

Treg frequency, phenotype, and intracellular lipid content were assessed ex vivo from FHBL2 subjects and age- and sex-matched controls, through multiparameter flow cytometry. The response of CD4 T cells from healthy controls to marked hypolipidemia was tested in vitro in low-lipid culture conditions.

RESULTS

The ex vivo analysis revealed that FHBL2 subjects showed higher percentages of Tregs with a phenotype undistinguishable from controls and with a lower lipid content, which directly correlated with the concentrations of circulating lipoproteins. In vitro, lipid restriction induced the upregulation of genes of the mevalonate pathway, including those involved in isoprenoid biosynthesis, and concurrently increased the expression of the Treg markers FOXP3 and Helios. The latter event was found to be prenylation-dependent, and likely related to increased IL-2 production and signaling.

CONCLUSIONS

Our study demonstrates that FHBL2 is characterized by high Treg frequencies, a feature which may concur to the reduced atherosclerotic risk in this condition. Mechanistically, hypolipidemia may directly favor Treg expansion, through the induction of the mevalonate pathway and the prenylation of key signaling proteins.

Circulating levels of PCSK9, ANGPTL3 and Lp(a) in stage III breast cancers

BACKGROUND / SYNOPSIS

Cholesterol and lipids play an important role in sustaining tumor growth and metastasis in a large variety of cancers. ANGPTL3 and PCSK9 modify circulating cholesterol levels, thus availability of lipids to peripheral cells. Little is known on the role, if any, of circulating lipid-related factors such as PCSK9, ANGPTL3 and lipoprotein (a) in cancers.

OBJECTIVE/PURPOSE

To compare circulating levels of PCSK9, ANGPTL3, and Lp(a) in women with stage III breast cancer versus women with premalignant or benign breast lesions.

METHODS

Twenty-three plasma samples from women diagnosed with a stage III breast cancer (ductal, lobular or mixed) were matched for age with twenty-three plasma samples from women bearing premalignant (stage 0, n = 9) or benign (n = 14) breast lesions. The lipid profile (Apo B, total cholesterol, HDL cholesterol and triglycerides levels) and Lp(a) were measured on a Roche Modular analytical platform, whereas LDL levels were calculated with the Friedewald formula. ANGPTL3 and PCSK9 plasma levels were quantitated by ELISA. All statistical analyses were performed using SAS software version 9.4.

RESULTS

PCSK9 levels were significantly higher in women with stage III breast cancer compared to age-matched counterparts presenting a benign lesion (95.9 ± 27.1 ng/mL vs. 78.5 ± 19.3 ng/mL, p < 0.05, n = 14). Moreover, PCSK9 levels positively correlated with breast disease severity (benign, stage 0, stage III) (Rho = 0.34, p < 0.05, n = 46). In contrast, ANGPTL3 and Lp(a) plasma levels did not display any association with breast disease status and lipids did not correlate with disease severity.

CONCLUSION

In this small cohort of 46 women, PCSK9 levels tended to increase with the severity of the breast disease. Given that PCSK9 plays an important role in maintaining cholesterolemia, and a potential role in tumor evasion, present results warrant further investigation into a possible association between PCSK9 levels and breast cancer severity in larger cohorts of women.

New and Emerging Therapies for Dyslipidemia

Atherosclerotic cardiovascular disease (ASCVD) continues to represent a growing global health challenge. Despite guideline-recommended treatment of ASCVD risk, including antihypertensive, high-intensity statin therapy, and antiaggregant agents, high-risk patients, especially those with established ASCVD and patients with type 2 diabetes, continue to experience cardiovascular events. Recent years have brought significant developments in lipid and atherosclerosis research. Several lipid drugs owe their existence, in part, to human genetic evidence. Here, the authors briefly review the mechanisms, the effect on lipid parameters, and safety profiles of some of the most promising new lipid-lowering approaches that will be soon available in our daily clinical practice.

A Modern Approach to Dyslipidemia

Lipid disorders involving derangements in serum cholesterol, triglycerides, or both are commonly encountered in clinical practice and often have implications for cardiovascular risk and overall health. Recent advances in knowledge, recommendations, and treatment options have necessitated an updated approach to these disorders. Older classification schemes have outlived their usefulness, yielding to an approach based on the primary lipid disturbance identified on a routine lipid panel as a practical starting point. Although monogenic dyslipidemias exist and are important to identify, most individuals with lipid disorders have polygenic predisposition, often in the context of secondary factors such as obesity and type 2 diabetes. With regard to cardiovascular disease, elevated low-density lipoprotein cholesterol is essentially causal, and clinical practice guidelines worldwide have recommended treatment thresholds and targets for this variable. Furthermore, recent studies have established elevated triglycerides as a cardiovascular risk factor, whereas depressed high-density lipoprotein cholesterol now appears less contributory than was previously believed. An updated approach to diagnosis and risk assessment may include measurement of secondary lipid variables such as apolipoprotein B and lipoprotein(a), together with selective use of genetic testing to diagnose rare monogenic dyslipidemias such as familial hypercholesterolemia or familial chylomicronemia syndrome. The ongoing development of new agents-especially antisense RNA and monoclonal antibodies-targeting dyslipidemias will provide additional management options, which in turn motivates discussion on how best to incorporate them into current treatment algorithms.

A novel nanobody-heavy chain antibody against Angiopoietin-like protein 3 reduces plasma lipids and relieves nonalcoholic fatty liver disease

Background

Nonalcoholic fatty liver disease (NAFLD) is a metabolic disease mainly on account of hypercholesterolemia and may progress to cirrhosis and hepatocellular carcinoma. The discovery of effective therapy for NAFLD is an essential unmet need. Angiopoietin-like protein 3 (ANGPTL3), a critical lipid metabolism regulator, resulted in increased blood lipids and was elevated in NAFLD. Here, we developed a nanobody-heavy chain antibody (VHH-Fc) to inhibit ANGPTL3 for NAFLD treatment.

Results

In this study, we retrieved an anti-ANGPTL3 VHH and Fc fusion protein, C44-Fc, which exhibited high affinities to ANGPTL3 proteins and rescued ANGPLT3-mediated inhibition of lipoprotein lipase (LPL) activity. The C44-Fc bound a distinctive epitope within ANGPTL3 when compared with the approved evinacumab, and showed higher expression yield. Meanwhile, C44-Fc had significant reduction of the triglyceride (~ 44.2%), total cholesterol (~ 36.6%) and LDL-cholesterol (~ 54.4%) in hypercholesterolemic mice and ameliorated hepatic lipid accumulation and liver injury in NAFLD mice model.

Conclusions

We discovered a VHH-Fc fusion protein with high affinity to ANGPTL3, strong stability and also alleviated the progression of NAFLD, which might offer a promising therapy for NAFLD.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01456-z.

New Therapies for Primary Hyperlipidemia

Primary hyperlipidemias include a heterogeneous set of monogenic and polygenic conditions characterized by a strong family aggregation, severe forms of hypercholesterolemia and/or hypertriglyceridemia, appearance early on life, and a high risk of cardiovascular events and/or recurrent pancreatitis. In real life, a small proportion of the primary hyperlipidemia cases is recognized and treated properly. Our goal is to present an update of current and upcoming therapies for patients with primary hyperlipidemia. Recently, new lipid-lowering medications have obtained authorization from the U.S. Food and Drug Administration and the European Medicines Agency. These drugs target metabolic pathways, including (adenosine 5'-triphosphates)-citrate lyase (bempedoic acid), proprotein convertase subtilisin/kexin 9 (inclisiran), apolipoprotein CIII (volanesorsen), and angiopoietin-like 3 (volanesorsen), that have additive effects with the actions of the currently available therapies (i.e., statins, ezetimibe or fibrates). We discuss the potential clinical indications for the novel medications. To conclude, the addition of these new medications to the therapeutic options for primary hyperlipidemia patients may increase the likelihood of achieving the treatment targets. Also, it could be a safer alternative for patients with side effects for the currently available drugs.

The Fibrinogen-like Domain of ANGPTL3 Facilitates Lipolysis in 3T3-L1 Cells by Activating the Intracellular Erk Pathway

Background: ANGPTL3 stimulates lipolysis in adipocytes, but the underlying molecular mechanism is yet unknown. The C-terminal fibrinogen-like domain of ANGPTL3 (ANGPTL3-Fld) activates the AKT pathway in endothelial cells. Hence, we evaluated whether ANGPTL3-Fld stimulates lipolysis in adipocytes through the MAPK kinase pathway. Materials and Methods: 3T3-L1 adipocytes were treated with isoproterenol (ISO), ANGPTL3-Fld, or both. Lipolysis was evaluated through the release of free fatty acids (FFAs) in the culture medium. The activation status of intracellular kinases was evaluated with and without the inhibition of the BRAF–ERK arm of the MAPK pathway. Results: ANGPTL3-Fld alone was not able to activate lipolysis, while the combination of ANGPTL3-Fld and ISO determined a 10-fold enrichment of the FFA concentration in the culture medium with an incremental effect (twofold) when compared with ISO alone. ANGPTL3-Fld alone inhibited hormone-sensitive lipase (HSL), whereas the treatment with ISO induced the activation of HSL. The net balance of ANGPTL3-Fld and ISO cotreatment resulted in HSL activation. The results indicate that ANGPTL3-Fld generated an intracellular activation signal involving the MAPK–ERK pathway, possibly through the PDGFRβ—PLCγ-AMPK axis. Conclusion: ANGPTL3-Fld appears to act as a facilitator of lipolysis in adipocytes, and this effect was driven by a signal mediated by a pathway that is different from the canonical β-adrenergic stimulus.

A Tale of Two New Targets for Hypertriglyceridaemia: Which Choice of Therapy?

Angiopoietin-like protein 3 (ANGPTL3) and apolipoprotein C-III (apoC-III) are novel metabolic targets for correcting hypertriglyceridaemia (HTG). As a background to their potential clinical use, we review the metabolic aetiology of HTG, particular abnormalities in triglyceride-rich lipoproteins (TRLs) and their role in atherosclerotic cardiovascular disease (ASCVD) and acute pancreatitis. Molecular and cardiometabolic aspects of ANGPTL3 and apoC-III, as well as inhibition of these targets with monoclonal antibody and nucleic acid therapies, are summarized as background information to descriptions and analyses of recent clinical trials. These studies suggest that ANGPTL3 and apoC-III inhibitors are equally potent in lowering elevated plasma triglycerides and TRLs across a wide range of concentrations, with possibly greater efficacy with inhibition of apoC-III. ANGPTL3 inhibition may, however, have the advantage of greater lowering of plasma LDL cholesterol and could specifically address elevated LDL cholesterol in familial hypercholesterolaemia refractory to standard drug therapies. Large clinical outcome trials in relevant populations are still required to confirm the long-term efficacy, safety and cost effectiveness of these potent agents for mitigating the complications of HTG. Beyond targeting severe chylomicronaemia in the prevention of acute pancreatitis, both agents could be useful in addressing residual risk of ASCVD due to TRLs in patients receiving best standard of care, including behavioural modifications, statins, ezetimibe, fibrates and proprotein convertase subtilisin/kexin type 9 inhibitors.

Angiopoietin-like proteins and postprandial partitioning of fatty acids

PURPOSE OF REVIEW

Over the last two decades, evolving discoveries around angiopoietin-like (ANGPTL) proteins, particularly ANGPTL3, ANGPTL4, and ANGPTL8, have generated significant interest in understanding their roles in fatty acid (FA) metabolism. Until recently, exactly how this protein family regulates lipoprotein lipase (LPL) in a tissue-specific manner to control FA partitioning has remained elusive. This review summarizes the latest insights into mechanisms by which ANGPTL3/4/8 proteins regulate postprandial FA partitioning.

RECENT FINDINGS

Accumulating evidence suggests that ANGPTL8 is an insulin-responsive protein that regulates ANGPTL3 and ANGPTL4 by forming complexes with them to increase or decrease markedly their respective LPL-inhibitory activities. After feeding, when insulin levels are high, ANGPTL3/8 secreted by hepatocytes acts in an endocrine manner to inhibit LPL in skeletal muscle, whereas ANGPTL4/8 secreted by adipocytes acts locally to preserve adipose tissue LPL activity, thus shifting FA toward the fat for storage. Insulin also decreases hepatic secretion of the endogenous ANGPTL3/8 inhibitor, apolipoprotein A5 (ApoA5), to accentuate ANGPTL3/8-mediated LPL inhibition in skeletal muscle.

SUMMARY

The ANGPTL3/4/8 protein family and ApoA5 play critical roles in directing FA toward adipose tissue postprandially. Selective targeting of these proteins holds significant promise for the treatment of dyslipidemias, metabolic syndrome, and their related comorbidities.

The role of lipid metabolism in shaping the expansion and the function of regulatory T cells

Metabolic inflammation, defined as a chronic low-grade inflammation, is implicated in numerous metabolic diseases. In recent years, the role of regulatory T cells (Tregs) as key controllers of metabolic inflammation has emerged, but our comprehension on how different metabolic pathways influence Treg functions needs a deeper understanding. Here we focus on how circulating and intracellular lipid metabolism, in particular cholesterol metabolism, regulates Treg homeostasis, expansion, and functions. Cholesterol is carried through the bloodstream by circulating lipoproteins (chylomicrons, very low-density lipoproteins, low-density lipoproteins). Tregs are equipped with a wide array of metabolic sensors able to perceive and respond to changes in the lipid environment through the activation of different intracellular pathways thus conferring to these cells a crucial metabolic and functional plasticity. Nevertheless, altered cholesterol transport, as observed in genetic dyslipidemias and atherosclerosis, impairs Treg proliferation and function through defective cellular metabolism. The intracellular pathway devoted to the cholesterol synthesis is the mevalonate pathway and several studies have shown that this pathway is essential for Treg stability and suppressive activity. High cholesterol concentrations in the extracellular environment may induce massive accumulation of cholesterol inside the cell thus impairing nutrients sensors and inhibiting the mevalonate pathway. This review summarizes the current knowledge regarding the role of circulating and cellular cholesterol metabolism in the regulation of Treg metabolism and functions. In particular, we will discuss how different pathological conditions affecting cholesterol transport may affect cellular metabolism in Tregs.

Selective targeting of angiopoietin-like 3 (ANGPTL3) with vupanorsen for the treatment of patients with familial partial lipodystrophy (FPLD): results of a proof-of-concept study

BACKGROUND

Familial partial lipodystrophy (FPLD) is a rare disease characterized by selective loss of peripheral subcutaneous fat, associated with dyslipidemia and diabetes mellitus. Reductions in circulating levels of ANGPTL3 are associated with lower triglyceride and other atherogenic lipids, making it an attractive target for treatment of FPLD patients. This proof-of-concept study was conducted to assess the efficacy and safety of targeting ANGPTL3 with vupanorsen in patients with FPLD.

METHODS

This was an open-label study. Four patients with FPLD (two with pathogenic variants in LMNA gene, and two with no causative genetic variant), diabetes (HbA1c ≥ 7.0 % and ≤ 12 %), hypertriglyceridemia (≥ 500 mg/dL), and hepatic steatosis (hepatic fat fraction, HFF ≥ 6.4 %) were included. Patients received vupanorsen subcutaneously at a dose of 20 mg weekly for 26 weeks. The primary endpoint was the percent change from baseline in fasting triglycerides at Week 27. Other endpoints analyzed at the same time point included changes in ANGPTL3, fasting lipids and lipoproteins, insulin secretion/sensitivity, postprandial lipids, and glycemic changes in response to a mixed meal test, HFF measured by MRI, and body composition measured by dual-energy absorptiometry (DEXA).

RESULTS

Baseline mean ± SD fasting triglyceride level was 9.24 ± 4.9 mmol/L (817.8 ± 431.9 mg/dL). Treatment resulted in reduction in fasting levels of triglycerides by 59.9 %, ANGPTL3 by 54.7 %, and in several other lipoproteins/lipids, including very low-density lipoprotein cholesterol by 53.5 %, non-high-density lipoprotein cholesterol by 20.9 %, and free fatty acids (FFA) by 41.7 %. The area under the curve for postprandial triglycerides, FFA, and glucose was reduced by 60 %, 32 %, and 14 %, respectively. Treatment with vupanorsen also resulted in 55 % reduction in adipose tissue insulin resistance index, while other insulin sensitivity indices and HbA1c levels were not changed. Additional investigations into HFF and DEXA parameters suggested dynamic changes in fat partitioning during treatment. Adverse events observed were related to common serious complications associated with diabetes and FPLD. Vupanorsen was well tolerated, and there was no effect on platelet count.

CONCLUSIONS

Although limited, these results suggest that targeting ANGPTL3 with vupanorsen could address several metabolic abnormalities in patients with FPLD.

New Frontiers in the Treatment of Homozygous Familial Hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) is a rare genetic disorder. The most common cause is a mutation in both alleles of the gene encoding for the low-density lipoprotein (LDL) receptor, although other causative mutations have been identified. Complications of atherosclerotic cardiovascular disease are common in these patients; therefore, reducing the elevated LDL-cholesterol burden is critical in their management. Conventionally, this is achieved by patients initiating lipid-lowering therapy, but this can present challenges in clinical practice. Fortunately, novel therapeutic strategies have enabled promising innovations in HoFH treatment. This review highlights recent and ongoing studies examining new therapeutic options for patients with HoFH.

Transcriptomic therapy for dyslipidemias utilizing nucleic acids targeted at ANGPTL3

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

High Density Lipoproteins: Is There a Comeback as a Therapeutic Target?

Low plasma levels of High Density Lipoprotein (HDL) cholesterol (HDL-C) are associated with increased risks of atherosclerotic cardiovascular disease (ASCVD). In cell culture and animal models, HDL particles exert multiple potentially anti-atherogenic effects. However, drugs increasing HDL-C have failed to prevent cardiovascular endpoints. Mendelian Randomization studies neither found any genetic causality for the associations of HDL-C levels with differences in cardiovascular risk. Therefore, the causal role and, hence, utility as a therapeutic target of HDL has been questioned. However, the biomarker "HDL-C" as well as the interpretation of previous data has several important limitations: First, the inverse relationship of HDL-C with risk of ASCVD is neither linear nor continuous. Hence, neither the-higher-the-better strategies of previous drug developments nor previous linear cause-effect relationships assuming Mendelian randomization approaches appear appropriate. Second, most of the drugs previously tested do not target HDL metabolism specifically so that the futile trials question the clinical utility of the investigated drugs rather than the causal role of HDL in ASCVD. Third, the cholesterol of HDL measured as HDL-C neither exerts nor reports any HDL function. Comprehensive knowledge of structure-function-disease relationships of HDL particles and associated molecules will be a pre-requisite, to test them for their physiological and pathogenic relevance and exploit them for the diagnostic and therapeutic management of individuals at HDL-associated risk of ASCVD but also other diseases, for example diabetes, chronic kidney disease, infections, autoimmune and neurodegenerative diseases.

Hypotriglyceridemias/hypolipidemias

Hypolipoproteinemias are characterized by a decrease in the plasma concentration of lipoproteins. Within them, we find two groups: hypobetalipoproteinemias (HBL), due to a decrease in the plasma concentration of lipoproteins containing apolipoprotein B, and hypoalphalipoproteinemias. Hypolipoproteinemias can be classified according to their origin, into primary and secondary. Primary HBLs are rare entities produced by mutations in different genes. So far, more than 140 mutations have been identified in the APOB, PCSK9, ANGPTL3, MTTP, and SAR1 genes. Early diagnosis and treatment are essential to avoid the development of serious complications. In this review we address the diagnosis and treatment of HBL, especially those in which there is hypotriglyceridemia.

Novel therapies for familial hypercholesterolemia

PURPOSE OF REVIEW

Familial hypercholesterolemia is a genetic disorder of defective clearance and subsequent increase in serum LDL cholesterol (LDL-C) with a resultant increased risk of premature atherosclerotic cardiovascular disease. Despite treatment with traditional lipid-lowering therapies (LLT), most patients with familial hypercholesterolemia are unable to achieve target LDL-C. We review current and future novel therapeutic options available for familial hypercholesterolemia.

RECENT FINDINGS

The use of proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitors are effective in lowering LDL-C in patients with familial hypercholesterolemia, with a reduction in LDL-C of 60% in heterozygous familial hypercholesterolemia (HeFH) and up to 35% in homozygous familial hypercholesterolemia (HoFH). Inclisiran, another novel agent, is a small-interfering ribonucleic acid that reduces hepatic production of PCSK9 to provide a prolonged and sustained reduction in LDL-C of nearly 50% in HeFH. However, both agents require LDL receptor (LDLR) activity. Evinacumab, a novel monoclonal antibody against angiopoetin-like 3 (ANGPTL3), reduces LDL-C by 50% independent of LDLR activity.

SUMMARY

Achieving a target LDL-C in familial hypercholesterolemia can be challenging with standard LLT; however, novel therapeutic modalities show remarkable reductions in LDL-C allowing nearly all patients with HeFH and a significant proportion of patients with HoFH to achieve acceptable LDL-C levels.

ANGPTL3 gene variants in subjects with familial combined hyperlipidemia

Angiopoietin-like 3 (ANGPTL3) plays an important role in lipid metabolism in humans. Loss-of-function variants in ANGPTL3 cause a monogenic disease named familial combined hypolipidemia. However, the potential contribution of ANGPTL3 gene in subjects with familial combined hyperlipidemia (FCHL) has not been studied. For that reason, the aim of this work was to investigate the potential contribution of ANGPTL3 in the aetiology of FCHL by identifying gain-of-function (GOF) genetic variants in the ANGPTL3 gene in FCHL subjects. ANGPTL3 gene was sequenced in 162 unrelated subjects with severe FCHL and 165 normolipemic controls. Pathogenicity of genetic variants was predicted with PredictSNP2 and FruitFly. Frequency of identified variants in FCHL was compared with that of normolipemic controls and that described in the 1000 Genomes Project. No GOF mutations in ANGPTL3 were present in subjects with FCHL. Four variants were identified in FCHL subjects, showing a different frequency from that observed in normolipemic controls: c.607-109T>C, c.607-47_607-46delGT, c.835+41C>A and c.*52_*60del. This last variant, c.*52_*60del, is a microRNA associated sequence in the 3′UTR of ANGPTL3, and it was present 2.7 times more frequently in normolipemic controls than in FCHL subjects. Our research shows that no GOF mutations in ANGPTL3 were found in a large group of unrelated subjects with FCHL.

Lipid Lowering Drugs: Present Status and Future Developments

Purpose of review

Based on the recent data of the DA VINCI study, it is clear that, besides utilization of statins, there is a need to increase non-statin lipid lowering approaches to reduce the cardiovascular burden in patients at highest risk.

Recent findings

For hypercholesterolemia, the small synthetic molecule bempedoic acid has the added benefit of selective liver activation, whereas inclisiran, a hepatic inhibitor of the PCSK9 synthesis, has comparable effects with PCSK9 monoclonal antibodies. For hypertriglyceridemia, cardiovascular benefit has been achieved by the use of icosapent ethyl, whereas results with pemafibrate, a selective agonist of PPAR-α, are eagerly awaited. In the era of RNA-based therapies, new options are offered to dramatically reduce levels of lipoprotein(a) (APO(a)L_RX) and of triglycerides (ANGPTL3L_RX and APOCIII-L_Rx).

Summary

Despite the demonstrated benefits of statins, a large number of patients still remain at significant risk because of inadequate LDL-C reduction or elevated blood triglyceride-rich lipoproteins or lipoprotein(a). The area of lipid modulating agents is still ripe with ideas and major novelties are to be awaited in the next few years.

The Interplay between Angiopoietin-Like Proteins and Adipose Tissue: Another Piece of the Relationship between Adiposopathy and Cardiometabolic Diseases?

Angiopoietin-like proteins, namely ANGPTL3-4-8, are known as regulators of lipid metabolism. However, recent evidence points towards their involvement in the regulation of adipose tissue function. Alteration of adipose tissue functions (also called adiposopathy) is considered the main inducer of metabolic syndrome (MS) and its related complications. In this review, we intended to analyze available evidence derived from experimental and human investigations highlighting the contribution of ANGPTLs in the regulation of adipocyte metabolism, as well as their potential role in common cardiometabolic alterations associated with adiposopathy. We finally propose a model of ANGPTLs-based adipose tissue dysfunction, possibly linking abnormalities in the angiopoietins to the induction of adiposopathy and its related disorders.

Angiopoietin-like protein 3, an emerging cardiometabolic therapy target with systemic and cell-autonomous functions

Angiopoietin like protein 3 (ANGPTL3) is best known for its function as an inhibitor of lipoprotein and endothelial lipases. Due to the capacity of genetic or pharmacologic ANGPTL3 suppression to markedly reduce circulating lipoproteins, and the documented cardioprotection upon such suppression, ANGPTL3 has become an emerging therapy target for which both antibody and antisense oligonucleotide (ASO) therapeutics are being clinically tested. While the antibody is relatively selective for circulating ANGPTL3, the ASO also depletes the intra-hepatocellular protein, and there is emerging evidence for cell-autonomous functions of ANGPTL3 in the liver. These include regulation of hepatocyte glucose and fatty acid uptake, insulin sensitivity, LDL/VLDL remnant uptake, VLDL assembly/secretion, polyunsaturated fatty acid (PUFA) and PUFA-derived lipid mediator content, and gene expression. In this review we elaborate on (i) why ANGPTL3 is considered one of the most promising new cardiometabolic therapy targets, and (ii) the present evidences for its intra-hepatocellular or cell-autonomous functions.

Hypertriglyceridemia-Causes, Significance, and Approaches to Therapy

Hypertriglyceridemia (HTG) is a common metabolic disorder with both genetic and lifestyle factors playing significant roles in its pathophysiology. HTG poses a risk for the development of cardiovascular disease (CVD) in the population at large and for pancreatitis in about two percent of individuals with extremely high levels of triglycerides (TG). This manuscript summarizes the mechanisms underlying the development of HTG as well as its management, including emerging therapies targeted at specific molecular pathways.