Highlights
- Olezarsen, a novel antisense oligonucleotide targeting APOC3, demonstrated potent biochemical efficacy by reducing triglycerides by approximately 64% and remnant cholesterol by 72%.
- The Essence-TIMI 73b imaging study found no significant change in the primary endpoint of non-calcified plaque volume (NCPV) at 12 months compared to placebo.
- The study highlights a potential dissociation between rapid biomarker improvement (triglycerides/remnants) and immediate structural changes in coronary anatomy on a background of standard-of-care lipid therapy.
- Future research must reconcile these imaging findings with long-term clinical outcome trials to determine the ultimate cardiovascular benefit of APOC3 inhibition.
Background
For decades, the “cholesterol hypothesis” has centered on the aggressive lowering of low-density lipoprotein cholesterol (LDL-C). However, even when LDL-C targets are achieved through statins and PCSK9 inhibitors, a substantial “residual inflammatory and lipid risk” remains. Much of this residual risk is attributed to triglyceride-rich lipoproteins (TRLs) and their remnants. Apolipoprotein C-III (apoC-III) has emerged as a critical regulator of TRL metabolism; it inhibits lipoprotein lipase (LPL) and hepatic uptake of remnants, effectively serving as a metabolic brake on triglyceride clearance.
Elevated levels of apoC-III are epidemiologically and genetically linked to an increased risk of coronary artery disease (CAD). Early clinical observations, such as those by Norum et al. (NEJM 1982), identified that familial deficiencies in apolipoproteins A-I and C-III were associated with precocious CAD, though the individual contributions of these proteins remained debated. Conversely, rare nonsense mutations that naturally lower apoC-III levels have been associated with lower triglyceride levels and reduced cardiovascular risk. Olezarsen is a liver-targeted antisense oligonucleotide designed to inhibit the production of apoC-III, thereby accelerating the clearance of TRLs and potentially reducing the atherosclerotic burden.
Key Content
Therapeutic Rationale: Targeting the ApoC-III Pathway
ApoC-III is primarily synthesized in the liver. By binding to APOC3 mRNA, olezarsen triggers its degradation, leading to a profound decrease in circulating apoC-III. This allows for increased LPL activity and enhanced clearance of remnant cholesterol. Prior phase 2 studies indicated that olezarsen could reduce triglycerides by over 60% without the adverse LDL-C elevations sometimes seen with other triglyceride-lowering agents. The Essence-TIMI 73b study was designed to transition from these biochemical observations to structural evidence, using coronary computed tomography angiography (CCTA) to measure plaque modulation.
Essence-TIMI 73b: Study Design and Methodology
The Essence-TIMI 73b trial was a randomized, double-blind, placebo-controlled imaging study. It enrolled 468 participants (349 in the olezarsen arm and 119 in the placebo arm) between November 2022 and February 2024. Key inclusion criteria included:
- Fasted triglycerides ≥150 mg/dL (median at baseline was 249 mg/dL).
- Established cardiovascular disease or high-risk status.
- The presence of identifiable non-calcified plaque on baseline CCTA.
Patients were predominantly well-managed on background therapies, with 97% receiving lipid-lowering agents (mostly high-intensity statins). The primary endpoint was the percent change from baseline to 12 months in non-calcified plaque volume (NCPV), a marker highly associated with vulnerable plaque and future clinical events.
Biochemical Results vs. Structural Outcomes
The biochemical results were robust and statistically significant. At the 6-month mark, olezarsen achieved:
- A 63.9% reduction in triglycerides over placebo.
- A 71.9% reduction in remnant cholesterol.
- A 16.0% reduction in apolipoprotein B (apoB).
- No significant change in LDL-C, confirming the drug’s specificity for TRL pathways.
However, despite this impressive lipid remodeling, the primary imaging endpoint was not met. The percent change in NCPV from baseline to month 12 did not differ significantly between the groups (placebo-adjusted least-squares mean difference 2.98%; 95% CI -3.4 to 9.3; p=0.36). Secondary endpoints, including changes in low-attenuation plaque (often associated with the necrotic core), calcified plaque, and total plaque volume, also showed no significant difference at the 12-month interval.
Methodological Advances in Plaque Imaging
This study utilized high-resolution CCTA, which has become the gold standard for non-invasive longitudinal plaque monitoring. Unlike intravascular ultrasound (IVUS), CCTA allows for the characterization of plaque composition (calcified vs. non-calcified) across the entire coronary tree. The lack of regression in Essence-TIMI 73b stands in contrast to studies like GLAGOV, where PCSK9 inhibition led to significant plaque regression. The discrepancy may lie in the specific atherogenic potential of remnants versus LDL particles, or perhaps the timeline required to see structural changes in patients already on optimized statin therapy.
Expert Commentary
The results of Essence-TIMI 73b present a complex challenge to the “remnant cholesterol hypothesis.” While the study proves that olezarsen is a powerful tool for correcting hypertriglyceridemia, the failure to reduce plaque volume within 12 months raises several critical questions for clinicians.
First, the 12-month duration may be insufficient. Atherosclerosis is a chronic, decadal process. While LDL-C lowering can lead to rapid lipid depletion from the plaque core, TRL-mediated risk might involve different pathways of inflammation and cholesterol deposition that require longer exposure to lower levels before structural regression is visible. Second, the “ceiling effect” of statins must be considered. When 97% of the cohort is already on lipid-lowering therapy, the marginal benefit of adding an APOC3 inhibitor on top of a stable plaque may be smaller than what would be seen in a statin-naive population.
Furthermore, we must look at the proteomic context. As discussed in the CASABLANCA study (JACC 2019), an HDL apolipoproteomic score including apoC-III is a strong predictor of CAD presence and cardiovascular death. This suggests that the role of apoC-III is not merely about the volume of lipid carried in TRLs, but perhaps the functionality of HDL and the inflammatory milieu. Reducing the volume of non-calcified plaque is only one way to stabilize a patient; it is possible that olezarsen improves plaque *quality* or reduces systemic inflammation in ways that CCTA volume measurements cannot fully capture.
Clinicians should also note the neutrality on LDL-C. In many triglyceride-lowering trials (such as those for fibrates or earlier antisense agents), a decrease in TRLs was often offset by a rise in LDL-C as VLDL was converted to LDL. Olezarsen’s ability to lower triglycerides and apoB without raising LDL-C is a significant pharmacological advantage, even if this specific imaging study was neutral.
Conclusion
The Essence-TIMI 73b study provides high-quality, randomized evidence that 12 months of APOC3 inhibition with olezarsen, while highly effective at lowering triglycerides and remnant cholesterol, does not significantly alter non-calcified coronary plaque volume in patients already receiving standard lipid-lowering therapy. This “neutral” structural result should not be interpreted as a lack of clinical utility. Historical data, such as the 1995 Japanese case study on apoA-I/apoC-III deficiency, remind us that the absence of massive plaque does not always correlate linearly with lipid levels.
The true test for olezarsen will be the ongoing Phase 3 cardiovascular outcome trials (CVOTs). Much like the history of ezetimibe—where imaging studies were often underwhelming but clinical outcomes eventually proved beneficial—the final verdict on APOC3 inhibition will depend on its ability to reduce myocardial infarctions and revascularizations over a multi-year follow-up. For now, olezarsen remains a promising agent for the management of severe hypertriglyceridemia, while its role in routine CAD prevention continues to evolve.
References
- Marston NA, et al. Effect of APOC3 Inhibition with Olezarsen on Coronary Atherosclerosis: Essence-TIMI 73b Imaging Study. Circulation. 2026-03-30. PMID: 41910513.
- Dullaart RPF, et al. Association of an HDL Apolipoproteomic Score With Coronary Atherosclerosis and Cardiovascular Death. J Am Coll Cardiol. 2019;73(17):2135-2145. PMID: 31047001.
- Norum RA, et al. Familial deficiency of apolipoproteins A-I and C-III and precocious coronary-artery disease. N Engl J Med. 1982;306(25):1513-1519. PMID: 7078608.
- Yamashita S, et al. A new case of apoA-I deficiency showing codon 8 nonsense mutation of the apoA-I gene without evidence of coronary heart disease. Arterioscler Thromb Vasc Biol. 1995;15(11):1866-1874. PMID: 7583566.
