Genetics of Triglyceride-Rich Lipoproteins Guide Identification of Pharmacotherapy for Cardiovascular Risk Reduction

The Emerging Potential of Apolipoprotein C-III Inhibition for ASCVD Prevention: A State-of-the-Art Review

PURPOSE OF REVIEW

Multiple agents are being developed that inhibit apolipoprotein (apo) C-III. This state-of-the-art review examines their potential for atherosclerotic cardiovascular disease (ASCVD) risk reduction.

RECENT FINDINGS

Apo C-III, an apolipoprotein on the surface of triglyceride-rich lipoproteins (TRLs), impairs clearance of TRLs through both lipoprotein lipase dependent and independent pathways, thereby resulting in increased concentrations of triglycerides. Apo C-III has also been shown to have pro-atherogenic effects when bound to high-density lipoprotein (HDL) particles. Classical and genetic epidemiology studies provide support for the concept that apo C-III is associated with an increased risk of ASCVD events. Drug efficacy of agents that silence APOC3 mRNA has been studied in populations with varying hypertriglyceridemia severity, including those with familial chylomicronemia syndrome, multifactorial chylomicronemia syndrome/severe hypertriglyceridemia, and mixed hyperlipidemia. Randomized controlled trials have reported significant reductions in TG and non-HDL cholesterol levels among these patients treated with APOC3 inhibitors. Upcoming clinical outcomes trials seek to establish a role for APOC3 inhibitors to reduce risk of ASCVD.

Evinacumab Reduces Triglyceride-Rich Lipoproteins in Patients with Hyperlipidemia: A Post-Hoc Analysis of Three Randomized Clinical Trials

PURPOSE

Natural selection (Mendelian randomization) studies support a causal relationship between elevated triglyceride-rich lipoproteins (TRLs) and atherosclerotic cardiovascular disease (ASCVD). This post-hoc analysis assessed the efficacy of evinacumab in reducing TRLs in patient cohorts from three separate clinical trials with evinacumab.

METHODS

Patients with homozygous familial hypercholesterolemia (HoFH) and low-density lipoprotein cholesterol (LDL-C) ≥ 70 mg/dL were enrolled in a phase III trial (R1500-CL-1629; NCT03399786). Patients diagnosed with refractory hypercholesterolemia, with LDL-C ≥ 70 mg/dL or ≥ 100 mg/dL for those with or without ASCVD, respectively, were enrolled in a phase II trial (R1500-CL-1643; NCT03175367). Patients with severe hypertriglyceridemia (fasting TGs ≥ 500 mg/dL) were enrolled in a phase II trial (R1500-HTG-1522; NCT03452228). Patients received evinacumab intravenously (5 or 15 mg/kg) every 4 weeks, or subcutaneously (300 or 450 mg) every week or every 2 weeks. Efficacy outcomes included change in TRLs (calculated as total cholesterol minus high-density lipoprotein cholesterol minus LDL-C) and other lipid parameters from baseline to 12, 16, or 24 weeks for trial 1522, 1643, and 1629, respectively.

RESULTS

At baseline, TRL levels were higher for patients with severe hypertriglyceridemia entering the 1522 trial vs. other cohorts. Reductions in TRLs were observed across all studies with evinacumab, with > 50% reduction from baseline observed at the highest doses evaluated in patients with HoFH or refractory hypercholesterolemia. Within all three trials, evinacumab was generally well tolerated.

CONCLUSIONS

Despite limitations in direct comparisons between study groups, these data indicate that TRL levels could be a future target for lipid-lowering therapies.

Severe hypertriglyceridemia: Existing and emerging therapies

Severe hypertriglyceridemia (sHTG), defined as a triglyceride (TG) concentration ≥ 500 mg/dL (≥ 5.7 mmol/L) is an important risk factor for acute pancreatitis. Although lifestyle, some medications, and certain conditions such as diabetes may lead to HTG, sHTG results from a combination of major and minor genetic defects in proteins that regulate TG lipolysis. Familial chylomicronemia syndrome (FCS) is a rare disorder caused by complete loss of function in lipoprotein lipase (LPL) or LPL activating proteins due to two homozygous recessive traits or compound heterozygous traits. Multifactorial chylomicronemia syndrome (MCS) and sHTG are due to the accumulation of rare heterozygous variants and polygenic defects that predispose individuals to sHTG phenotypes. Until recently, treatment of sHTG focused on lifestyle interventions, control of secondary factors, and nonselective pharmacotherapies that had modest TG-lowering efficacy and no corresponding reductions in atherosclerotic cardiovascular disease events. Genetic discoveries have allowed for the development of novel pathway-specific therapeutics targeting LPL modulating proteins. New targets directed towards inhibition of apolipoprotein C-III (apoC-III), angiopoietin-like protein 3 (ANGPTL3), angiopoietin-like protein 4 (ANGPTL4), and fibroblast growth factor-21 (FGF21) offer far more efficacy in treating the various phenotypes of sHTG and opportunities to reduce the risk of acute pancreatitis and atherosclerotic cardiovascular disease events.

Clinical Trial Design for Triglyceride-Rich Lipoprotein-Lowering Therapies: JACC Focus Seminar 3/3

Triglyceride-rich lipoproteins (TRLs) are a source of residual risk in patients with atherosclerotic cardiovascular disease, and are indirectly correlated with triglyceride (TG) levels. Previous clinical trials studying TG-lowering therapies have either failed to reduce major adverse cardiovascular events or shown no linkage of TG reduction with event reduction, particularly when these agents were tested on a background of statin therapy. Limitations in trial design may explain this lack of efficacy. With the advent of new RNA-silencing therapies in the TG metabolism pathway, there is renewed focus on reducing TRLs for major adverse cardiovascular event reduction. In this context, the pathophysiology of TRLs, pharmacological effects of TRL-lowering therapies, and optimal design of cardiovascular outcomes trials are major considerations.

Phenome-wide Mendelian randomization study of plasma triglyceride levels and 2600 disease traits

Background

Causality between plasma triglyceride (TG) levels and atherosclerotic cardiovascular disease (ASCVD) risk remains controversial despite more than four decades of study and two recent landmark trials, STRENGTH, and REDUCE-IT. Further unclear is the association between TG levels and non-atherosclerotic diseases across organ systems.

Methods

Here, we conducted a phenome-wide, two-sample Mendelian randomization (MR) analysis using inverse-variance weighted (IVW) regression to systematically infer the causal effects of plasma TG levels on 2600 disease traits in the European ancestry population of UK Biobank. For replication, we externally tested 221 nominally significant associations (p<0.05) in an independent cohort from FinnGen. To account for potential horizontal pleiotropy and the influence of invalid instrumental variables, we performed sensitivity analyses using MR-Egger regression, weighted median estimator, and MR-PRESSO. Finally, we used multivariable MR (MVMR) controlling for correlated lipid fractions to distinguish the independent effect of plasma TG levels.

Results

Our results identified seven disease traits reaching Bonferroni-corrected significance in both the discovery (p<1.92 × 10-5) and replication analyses (p<2.26 × 10-4), suggesting a causal relationship between plasma TG levels and ASCVDs, including coronary artery disease (OR 1.33, 95% CI 1.24-1.43, p=2.47 × 10-13). We also identified 12 disease traits that were Bonferroni-significant in the discovery or replication analysis and at least nominally significant in the other analysis (p<0.05), identifying plasma TG levels as a novel potential risk factor for nine non-ASCVD diseases, including uterine leiomyoma (OR 1.19, 95% CI 1.10-1.29, p=1.17 × 10-5).

Conclusions

Taking a phenome-wide, two-sample MR approach, we identified causal associations between plasma TG levels and 19 disease traits across organ systems. Our findings suggest unrealized drug repurposing opportunities or adverse effects related to approved and emerging TG-lowering agents, as well as mechanistic insights for future studies.

Funding

RD is supported by the National Institute of General Medical Sciences of the National Institutes of Health (NIH) (R35-GM124836) and the National Heart, Lung, and Blood Institute of the NIH (R01-HL139865 and R01-HL155915).

Association Between Triglycerides and Incident Cognitive Impairment in Black and White Adults in the Reasons for Geographic and Racial Differences in Stroke Study

Background Elevated nonfasting triglycerides were associated with non-Alzheimer dementia in a recent study. However, this study neither evaluated the association of fasting triglycerides with incident cognitive impairment (ICI) nor adjusted for high-density lipoprotein cholesterol or hs-CRP (high-sensitivity C-reactive protein), known risk markers for ICI and dementia. Methods and Results We examined the association between fasting triglycerides and ICI among 16 170 participants in the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study without cognitive impairment or a history of stroke at baseline in 2003 to 2007 and who had no stroke events during follow-up through September 2018. Overall, 1151 participants developed ICI during the median follow-up of 9.6 years. The relative risk for ICI associated with fasting triglycerides of ≥150 mg/dL versus <100 mg/dL including adjustment for age and geographic region of residence was 1.59 (95% CI, 1.20-2.11) among White women and 1.27 (95% CI, 1.00-1.62) among Black women. After multivariable adjustment, including adjustment for high-density lipoprotein cholesterol and hs-CRP, the relative risk for ICI associated with fasting triglycerides ≥150 mg/dL versus <100 mg/dL was 1.50 (95% CI, 1.09-2.06) among White women and 1.21 (95% CI, 0.93-1.57) among Black women. There was no evidence of an association between triglycerides and ICI among White or Black men. Conclusions Elevated fasting triglycerides were associated with ICI in White women after full adjustment including high-density lipoprotein cholesterol and hs-CRP. The current results suggest that the association between triglycerides and ICI is stronger in women than men.

Evinacumab in severe hypertriglyceridemia with or without lipoprotein lipase pathway mutations: a phase 2 randomized trial

Severe hypertriglyceridemia (sHTG) is an established risk factor for acute pancreatitis. Current therapeutic approaches for sHTG are often insufficient to reduce triglycerides and prevent acute pancreatitis. This phase 2 trial ( NCT03452228 ) evaluated evinacumab (angiopoietin-like 3 inhibitor) in three cohorts of patients with sHTG: cohort 1, familial chylomicronemia syndrome with bi-allelic loss-of-function lipoprotein lipase (LPL) pathway mutations (n = 17); cohort 2, multifactorial chylomicronemia syndrome with heterozygous loss-of-function LPL pathway mutations (n = 15); and cohort 3, multifactorial chylomicronemia syndrome without LPL pathway mutations (n = 19). Fifty-one patients (males, n = 27; females, n = 24) with a history of hospitalization for acute pancreatitis were randomized 2:1 to intravenous evinacumab 15 mg kg-1 or placebo every 4 weeks over a 12-week double-blind treatment period, followed by a 12-week single-blind treatment period. The primary end point was the mean percent reduction in triglycerides from baseline after 12 weeks of evinacumab exposure in cohort 3. Evinacumab reduced triglycerides in cohort 3 by a mean (s.e.m.) of -27.1% (37.4) (95% confidence interval -71.2 to 84.6), but the prespecified primary end point was not met. No notable differences in adverse events between evinacumab and placebo treatment groups were seen during the double-blind treatment period. Although the primary end point of a reduction in triglycerides did not meet the prespecified significance level, the observed safety and changes in lipid and lipoprotein levels support the further evaluation of evinacumab in larger trials of patients with sHTG. Trial registration number: ClinicalTrials.gov NCT03452228 .

There is urgent need to treat atherosclerotic cardiovascular disease risk earlier, more intensively, and with greater precision: A review of current practice and recommendations for improved effectiveness

Atherosclerotic cardiovascular disease (ASCVD) is epidemic throughout the world and is etiologic for such acute cardiovascular events as myocardial infarction, ischemic stroke, unstable angina, and death. ASCVD also impacts risk for dementia, chronic kidney disease peripheral arterial disease and mobility, impaired sexual response, and a host of other visceral impairments that adversely impact the quality and rate of progression of aging. The relationship between low-density lipoprotein cholesterol (LDL-C) and risk for ASCVD is one of the most highly established and investigated issues in the entirety of modern medicine. Elevated LDL-C is a necessary condition for atherogenesis induction. Basic scientific investigation, prospective longitudinal cohorts, and randomized clinical trials have all validated this association. Yet despite the enormous number of clinical trials which support the need for reducing the burden of atherogenic lipoprotein in blood, the percentage of high and very high-risk patients who achieve risk stratified LDL-C target reductions is low and has remained low for the last thirty years. Atherosclerosis is a preventable disease. As clinicians, the time has come for us to take primordial and primary prevention more serously. Despite a plethora of therapeutic approaches, the large majority of patients at risk for ASCVD are poorly or inadequately treated, leaving them vulnerable to disease progression, acute cardiovascular events, and poor aging due to loss of function in multiple visceral organs. Herein we discuss the need to greatly intensify efforts to reduce risk, decrease disease burden, and provide more comprehensive and earlier risk assessment to optimally prevent ASCVD and its complications. Evidence is presented to support that treatment should aim for far lower goals in cholesterol management, should take into account many more factors than commonly employed today and should begin significantly earlier in life.

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.

New Therapies for Lowering Triglyceride-Rich Lipoproteins: JACC Focus Seminar 3/4

Emerging evidence suggests that elevated concentrations of triglyceride-rich lipoprotein remnants (TRLs) derived from hepatic and intestinal sources contribute to the risk of atherosclerotic cardiovascular events. Natural selection studies support a causal role for elevated concentrations of remnant cholesterol and the pathways contributing to perturbations in metabolic pathways regulating TRLs with an increased risk of atherosclerotic cardiovascular disease events. New therapies targeting select catalytic pathways in TRL metabolism reduce atherosclerosis in experimental models, and concentrations of TRLs in patients with a vast range of triglyceride levels. Clinical trials with inhibitors of angiopoietin-like 3 protein and apolipoprotein C-III will be required to provide further guidance on the potential contribution of these emerging therapies in the paradigm of cardiovascular risk management in patients with elevated remnant cholesterol.