Lowering of TGs is today still best accomplished by peroxisomal proliferator-associated receptor (α, β, and γ) activation. Fibrates, the most effective activators of the PPARα system, generally have a mixed PPARα, β activity [
77]. PPARs belong to the nuclear hormone receptor superfamily and, by binding to PPAR-response regulatory elements (PPRE) heterodimerize with the retinoid X receptor (RXR) thus modulating genes involved in adipogenesis, lipid metabolism, inflammation, and control/maintenance of metabolic homeostasis [
78,
79]. Among fibrates, fenofibrate is mainly active on PPARα whereas bezafibrate acts on PPARα-β/δ, glitazones acting instead on PPARγ . By this mechanism, fibrates down-regulate apolipoprotein-CIII (apo-CIII) while stimulating the lipoprotein lipase gene expression thus affecting TG metabolism [
80].
Among PPARs, PPARα (also called NR1C1) is activated mainly under energy deprivation, in particular during fasting [
81], PPARα -mediated fatty acid catabolism is crucial for the synthesis of metabolites to be used as energy sources to other tissues such as ketone bodies in the brain [
82]. In addition to activating a number of genes in the FA β-oxidation pathway, e.g., carnitine palmitoyl transferase 1A and 2, PPARα also exerts an anti-inflammatory activity in mouse models, although contrasting data have been reported [
83].
Pemafibrate
Currently, there is growing interest in the selective activation of PPARα. Newly available PPARα agonists may provide an advancement, since older fibrates have a relatively weak activity and display limited efficacy due to elevation of transaminase, homocysteine, and creatinine with consequent, although rare, myopathy. The increased selectivity of PPARα is best exemplified by pemafibrate (previously known as K877), >2,000-fold more selective for PPARα vs either PPARγ or δ [
84,
85]. Clinical evaluation confirmed the extremely low active doses (0.1–0.2 mg bid) compared to fenofibrate (106.6 mg qd). A comparative trial over 24 weeks showed TG reductions of 46% for pemafibrate vs −39.7% for fenofibrate [
86]. This finding was confirmed in a number of further trials, also indicating that adverse events were less frequent vs fenofibrate 200 mg/day [
87]. The use of pemafibrate was also proposed for the handling of residual dyslipidemia for patients with TG>300 mg/dL on statins. Regardless of statin background combination therapy, pemafibrate 0.2–0.4 mg/day led to TG reductions of about 50% from baseline [
88]. These very positive findings have led to the planning of the PROMINENT (Pemafibrate to Reduce Cardiovascular Outcomes by Reducing Triglycerides in Patients with Diabetes) trial involving high ASCVD risk patients with in use of T2DM on statin therapy and who persist with atherogenic dyslipidemia. The primary end-point is the time of occurrence of the first non-fatal MI, ischemic stroke, unstable angina or coronary revascularization, and CV deaths [
47]. Two studies in Europe and the USA are currently ongoing in patients with severe hypertriglyceridemia (Table
2).
Table 2
Ongoing or recently completed studies involving inhibition of agents reducing triglyceride-rich lipoproteins
Pemafibrate | NCT03011450 (phase 3, in Europe) and NCT03001817 (phase 3, in US) | Study to evaluate the efficacy and safety of K-877 in adult patients with fasting high triglyceride levels and mild or moderate renal impairment |
Evinacumab (mAb against ANGPTL3) | NCT04233918 (phase 3) | Evaluating the efficacy and safety of evinacumab in pediatric patients with homozygous familial hypercholesterolemia |
NCT03452228 (phase 2) | Safety and efficacy following repeat-dose of evinacumab (Anti-ANGPTL3) in patients with severe hypertriglyceridemia (sHTG) at risk for acute pancreatitis |
NCT03409744 (phase 3) | Evaluate the long-term safety and efficacy of evinacumab in patients with homozygous familial hypercholesterolemia |
Vupanorsen (ANGPTL3-LRx) | NCT04516291 (phase 2) | A dose-ranging study with vupanorsen (TRANSLATE-TIMI 70) |
NCT04459767 (phase 1) | Investigation of safety, tolerability, pharmacokinetics and pharmacodynamics of single doses of vupanorsen in Japanese healthy adult participants with elevated triglycerides |
ARO-ANG3 (silencing RNA) | NCT03747224 (phase 1) | Study of ARO-ANG3 in healthy volunteers and in dyslipidemic patients |
AKCEA-APOCIII-LRx | NCT04568434 (phase 3) | A study of administered to patients with familial chylomicronemia syndrome (FCS) (BALANCE) |
NCT03385239 (phase 2) | Study of ISIS 678354 (AKCEA-APOCIII-LRx) in patients with hypertriglyceridemia and established cardiovascular disease (CVD) |
ARO-APOC3 (silencing RNA) | NCT03783377 (phase 1) | Study of ARO-APOC3 in healthy volunteers, hypertriglyceridemic patients and patients with familial chylomicronemia syndrome (FCS) |
Omega-3
The latest development in the treatment in hypertriglyceridemias has been the unexpected CV effectiveness of FA of the n-3 series (i.e., with multiple double bonds, the first being in the n-3 position from the terminal methyl group). These omega-3s act as “fraudulent fatty acids” [
89], i.e., they, somewhat similar to drugs with the FA-like structure, particularly fibrates, do not follow the liver metabolic handling by the classical fatty acetyl CoA oxidative mechanism with carnitine-mediated transport to mitochondria [
90]. They exert, instead, a moderate stimulation of the PPARα -mediated pathway, although peroxisomal proliferation is less extensive than in the case of fibrates [
91]. Clinical trials in patients given elevated daily doses of omega-3 in the form of TG or more recently of ethyl esters of eicosapentaenoic (EPA) or docosaexaenoic (DHA) acid, as well as with novel formulations of separated fatty acids, repeatedly confirmed an effective activity in TG reduction, particularly in patients with diabetes [
92]. A general review on the mechanisms of omega-3 involves targeting of characteristics of the metabolic syndrome, i.e., raised adipocyte differentiation, reduced lipolysis and lipogenesis and, more recently, reduced inflammatory changes in the adipose tissue, characteristic of obesity [
93]. Recent evidence has, however, provided exciting observations from a clinical trial on high dose EPA. The REDUCE-IT trial involved 8,179 participants with high CV risk (71% with established CV disease and 58% with T2DM). These had essentially normal LDL-C upon optimal statin treatment (75 mg/dL) whereas mean TG levels were moderately elevated (median value 216 mg /dL). Patients receiving 4 g of icosapent ethyl per day (2 g bid with meals) vs placebo for a median follow-up of 4.9 years had an absolute between group difference in primary CV endpoints of 4.8% vs placebo with a number needed to treat of 21 [
94]. Interestingly, a subsequent evaluation of the trial reported a significant decrement in the first and total CV deaths [
95]: total primary endpoint events (CV death, nonfatal myocardial infarction, nonfatal stroke, coronary revascularization, or hospitalization for unstable angina) were decreased by 30% and total key secondary endpoint events (cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke) by 28%. Findings of the REDUCE-IT trial indicate that TG reduction (e.g., −18.3% fall from baseline to 1 year) may be an important target of therapy, although possibly not all the benefits reported in the trial are explained by TG lowering. This tentative conclusion is supported by the recently reported EVAPORATE (Effect of Vascepa on Improving Coronary Atherosclerosis in People With High Triglycerides Taking Statin Therapy) trial in 80 coronary artery disease patients. They were allocated into two groups given a similar dose of EPA as in the REDUCE-IT trial or a placebo and followed for 18 months. Coronary computed tomographic scans showed that icosapent ethyl was superior to placebo in reducing plaque volume (primary endpoint) by 17%, fibrofatty and fibrous plaques by −34% and by −20%, respectively, whereas dense calcium did not change between groups [
96].
Differently from the icosapent ethyl formulation, daily administration of 4 g of the carboxylic acid formulation of EPA and DHA, in patients with hypertriglyceridemia (
> 240 mg/dL) and or diabetes (70%) resulted in neutral effects on CV prevention compared to corn oil (placebo). Despite a −20% reduction in TG and hsCRP, the HR for MACE (a composite of CV death, nonfatal MI, nonfatal stroke, coronary revascularization, or unstable angina requiring hospitalization) was 0.99 (95%CI 0.90–1.09). The STRENGTH (The Long-Term Outcomes Study to Assess Statin Residual Risk with Epanova in High Cardiovascular Risk Patients with Hypertriglyceridemia), recruiting 13,078 patients, was halted prematurely when it became apparent that the probability of clinical benefit was likely to be low. An increased rate of new-onset atrial fibrillation (HR 1.69, 95%CI 1.29–2.21) and of gastrointestinal adverse events [
97] was observed. Compared to the REDUCE-IT study, the achieved EPA levels in plasma and red blood cells were lower but it is uncertain whether these differences would be sufficient to explain the impact on MACE. The question as to whether possible deleterious effects of DHA in STRENGTH or the use of mineral oil in REDUCE-IT, with the potential of the latter to raise LDL-C and hsCRP, could be responsible for the different findings remains to be determined [
98] although data from comparative trials suggest no significant impact of mineral oil on CV outcomes [
99].
ANGPTL3 and Apo C-III Inhibition
In addition to evinacumab, antisense oligonucleotides (ASOs) targeting ANGPTL3 messenger RNA are under clinical evaluation. ANGPTL3-L
Rx, a second-generation ASO drug targeting ANGPTL3 mRNA, has a covalent linkage with the GalNAc cluster, conferring high affinity for the hepatocyte-specific asialoglycoprotein receptor (reviewed in [
40]).
A phase 1 trial aimed at testing the safety, pharmacokinetics, and pharmacodynamics of single ascending doses and multiple ascending doses of ANGPTL3-L
RX (vupanorsen) in healthy volunteers showed that this last was the regimen to be used. Once a week injection for 6 weeks of active compound reduced, at day 43, the circulating levels of ANGPTL3 from baseline by 46.6% (10 mg), 72.5% (20 mg), 81.3% (40 mg), and 84.5% (60 mg). Compared to placebo (0.9% sterile saline s.c.), ANGPTL3-L
RX lowered TG (from −33.2 to −63.1%), LDL-C (from −1.3 to −32.9%), VLDL-C (from −27.9 to −60%), non-HDL-C (from −10 to −36.6%), apoB (from −3.4 to −25.7%), and apolipoprotein (apo)C-III (from −18.9 to −58.8%). No clinical signs of prothrombotic effects, bleeding episodes, and significant decreases in platelet counts and liver or renal function damages were found ([
100]).
In a recent phase 2 trial, enrolling 105 patients with median TG levels of 252 mg/dL and T2DM, vupanorsen reduced ANGPTL3 by 41% (40 mg Q4W), 59% (80 mg Q4W), and 56% (20 mg QW) leading to a dramatic reduction in TG levels, −36% (40 mg Q4W), −53% (80 mg Q4W), and −47% (20 mg QW). Six months of treatment allowed most of the patients to reach TG levels < 150 mg/dL: 35% (40 mg Q4W), 58% (80 mg Q4W), and 39% (20 mg QW). At the dose of 80 mg Q4W, ANGPTL3 was reduced by 62%, apoC-III by 58%, remnant cholesterol (and VLDL-C) by 38%, non-HDL-C by 18%, TC by 19%, apoB by 9%, and HDL-C by 24%. Changes in LDL-C (−12%) were found only in patients given the dose of 20 mg QW. The most frequent adverse effects were injection-site pruritus and erythema, whereas no one experienced a confirmed platelet count <100,000/mm
3 [
101••].
Besides ANGPTL3, another recently approached target for the treatment of severe hypertriglyceridemia is provided by inhibitors of apo C-III, a multifaceted protein in cardiometabolic disease [
102]. Apo C-III is an inhibitor of LPL and has been recently identified as a risk factor for CV disease [
103,
104]. Apo C-III is a small molecule with a molecular weight of 8.8 kDa and 79 amino-acids, rapidly exchanged postprandially between lipoproteins [
105]. Indeed, all lipoproteins may contain ApoC-III, although this apoprotein is mainly represented in chylomicrons, VLDL, their remnants, and HDL. The clinical observation of apo C-III mutations with significant loss-of-function and associated with low TGs and elevated HDL has been reported in a number of studies [
106]. The lead investigators described a potential therapeutic approach to hypertriglyceridemia based on an inhibited activity of apo C-III (reviewed in [
107]).
At present, the only reported effective strategy is by administration of an antisense oligonucleotide, although monoclonal antibodies STT505 and STT5058 seemed to lower apo C-III levels and promote clearance of TG-rich lipoproteins in mice [
108].
The antisense inhibition was first evaluated by Gaudet et al. in patients with triglyceridemia between 350 and 2,000 mg/dL on stable fibrate therapy. Volanesorsen at doses from 100 to 300 mg once weekly for 13 weeks led to dose-dependent reductions of apoC-III (from −40 to −79.6%) concomitant with dramatic TG reductions (from 31.3 to 70.9%) [
109]. A larger study was conducted on 66 patients with familial chylomicronemia syndrome (FCS) treated for 52 weeks. Volanesorsen dramatically reduced apoC-III levels by 84% and mean TG by 77%, allowing after 3 months 77% of the patients to achieve TG levels ≤ 750 mg/dL. However, 14 patients given volanesorsen did not terminate the trial due to platelet count reductions [
110]. In spite of this drawback, the European Medical Agency (EMA) considered positively the benefit: risk ratio thus authorizing volanesorsen for the treatment of FCS. A recent meta-analysis of the available phase 2 and phase 3 clinical studies reported that volenesorsen significantly reduced VLDL-C (−73%), TG (−68%), ApoCIII (−74%), and raised HDL (+40%) and LDL-C (+47%, p= 0.057). Specifically, looking at LDL-C, it is worth mentioning that although in the APPROACH study the rise in LDL-C was +136%, the basal LDL-C levels were very low 28±19 mg/dL to become 61±39 mg/dL, still remaining in the normal range [
110]. Overall, the increment in LDL-C may be consequent to an enhanced conversion of VLDL to LDL or due to changes in the secretion and catabolism of the LDL particles, although changes in CETP activity cannot be excluded [
111].
Injection of volanesorsen was associated with a significantly higher risk of injection site reactions (OR= 32.89, 95%CI= 7.97–135.74) when compared to placebo [
112].
Recently, a new GalNac-conjugated APOCIII-L
Rx was tested in a dose-escalation Phase 1/2a study in healthy volunteers. A large improvement in the atherogenic lipid profile was detected both following a single-dose- or a multi-dose-regimen. This last choice led to median reductions of apoC-III by 66% (15 mg QW4), 84% (30 mg QW4), and by 89% (60 mg QW4) and of TG by 59%, 73%, and 66%, respectively. No flu-like reactions, platelet count reductions, liver, or renal safety signals were reported [
113,
114].