Application of Proprotein Convertase Subtilisin/Kexin Type 9 Inhibitor, Evolocumab, in Patients with Severe Hypertriglyceridemia
Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors have emerged as a promising class of drugs for managing dyslipidemia, particularly in reducing low-density lipoprotein cholesterol (LDL-c). Evolocumab, a PCSK9 inhibitor, binds to PCSK9 in plasma, preventing the degradation of the PCSK9-LDL receptor complex, thereby enhancing LDL receptor availability and reducing LDL-c levels. Beyond its LDL-lowering effects, PCSK9 inhibitors have also been shown to modestly reduce triglycerides (TG) by approximately 8% to 17% in the general population. However, their efficacy in patients with severe hypertriglyceridemia (HTG) remains less explored. This article presents a detailed analysis of the application of evolocumab in three patients with severe HTG, highlighting its potential role in managing this challenging condition.
Background and Mechanism of PCSK9 Inhibitors
PCSK9 inhibitors function by binding to PCSK9, a protein that promotes the degradation of LDL receptors in the liver. By inhibiting PCSK9, these drugs increase the number of LDL receptors on hepatocytes, enhancing the clearance of LDL-c from the bloodstream. While their primary indication is for LDL-c reduction, studies have also demonstrated a secondary effect on TG levels. This dual action makes PCSK9 inhibitors a potentially valuable therapeutic option for patients with severe HTG, particularly those who do not respond adequately to conventional lipid-lowering therapies such as statins, fibrates, and omega-3 fatty acids.
Case Presentations and Treatment Outcomes
Patient 1
A 38-year-old male with a body mass index (BMI) of 30.1 kg/m² was admitted for acute coronary syndrome, complicated by hypertension and type 2 diabetes. His highest recorded TG level was 29.94 mmol/L. Despite treatment with fenofibrate and atorvastatin, his lipid levels remained poorly controlled. Evolocumab 140 mg biweekly was initiated on June 4, 2020. Whole-exome sequencing (WES) revealed heterozygous mutations in the LPL gene (rs3735959 and rs316). Following the addition of evolocumab, the patient experienced a significant reduction in TG levels, with a stable decrease of approximately 70%.
Patient 2
A 61-year-old female with a BMI of 20.7 kg/m² had a long history of recurrent acute pancreatitis and HTG, with a peak TG level of 52.96 mmol/L. She had been on fenofibrate since 2004 and atorvastatin since 2017, with suboptimal results. Evolocumab 140 mg biweekly was added to her regimen on May 20, 2019. WES identified a homozygous mutation in the APOA5 gene (rs2075291) and multiple mutations in the LMF1 gene, both of which are associated with TG metabolism. With evolocumab, her TG levels decreased by 41.41% to 71.46%, demonstrating a relatively stable therapeutic effect.
Patient 3
A 40-year-old male with a BMI of 23.9 kg/m² was diagnosed with HTG during a routine physical examination in 2015. He experienced episodes of high triglyceride acute pancreatitis (HTG-AP) in 2016 and 2018. Despite treatment with fenofibrate and simvastatin, his TG levels fluctuated significantly, particularly in response to dietary changes. Evolocumab 140 mg biweekly was introduced on December 6, 2019. WES revealed heterozygous mutations in the LMF1 (rs181731943) and ANGPTL8 (rs192460764) genes. When the patient adhered to a light diet, evolocumab effectively controlled his TG levels, achieving an approximate 84% reduction.
Genetic Analysis and Classification of HTG
Whole-exome sequencing was performed on all three patients to identify genetic mutations contributing to their hyperlipidemia. The results revealed mutations in several genes associated with TG metabolism, including LPL, APOA5, LMF1, ANGPTL8, and GPIHBP1. Based on the new classification criteria for HTG and chylomicronemia, all three cases were classified as polygenic chylomicronemia (World Health Organization type 5). This classification underscores the complex genetic underpinnings of severe HTG and highlights the potential role of PCSK9 inhibitors in managing such cases.
Efficacy and Safety of Evolocumab in Severe HTG
In all three patients, the addition of evolocumab led to significant reductions in TG levels, regardless of the presence of HTG-related genetic mutations. The reductions ranged from 41.41% to 84%, which is notably higher than the 8% to 17% reduction observed in the general population. This suggests that the TG-lowering effect of PCSK9 inhibitors may be more pronounced in patients with severe HTG, possibly due to their higher baseline TG levels. Importantly, none of the patients experienced adverse effects related to evolocumab during the treatment period, underscoring its safety profile in this population.
Comparison with Conventional Lipid-Lowering Therapies
Current lipid-lowering therapies for HTG include statins, omega-3 fatty acids, and fibrates. Statins primarily target LDL-c reduction, with a modest effect on TG levels (5% to 15% reduction). Omega-3 fatty acids, particularly icosapent ethyl, have shown a more significant TG-lowering effect (approximately 20%) but are limited to specific formulations. Fibrates, while effective in some cases, are often inadequate for patients with genetic mutations affecting TG metabolism. In contrast, PCSK9 inhibitors like evolocumab offer a dual benefit of reducing both LDL-c and TG levels, making them a potentially valuable addition to the therapeutic arsenal for severe HTG.
Limitations and Future Directions
While the findings from these three cases are promising, several limitations must be acknowledged. The small sample size limits the generalizability of the results, and further studies with larger cohorts are needed to confirm the efficacy and safety of PCSK9 inhibitors in severe HTG. Additionally, the mechanism by which PCSK9 inhibitors reduce TG levels remains incompletely understood and warrants further investigation. The high cost of PCSK9 inhibitors may also limit their widespread use, particularly in resource-limited settings.
Conclusion
The application of evolocumab in three patients with severe HTG demonstrated significant reductions in TG levels, even in the presence of genetic mutations associated with hyperlipidemia. These findings suggest that PCSK9 inhibitors may be a valuable therapeutic option for managing severe HTG, particularly in patients who do not respond adequately to conventional therapies. However, further research is needed to elucidate the underlying mechanisms, confirm the safety and efficacy in larger populations, and address cost-related barriers to access. The potential of PCSK9 inhibitors to broaden their indications for lipid management underscores the importance of continued investigation into their role in treating complex lipid disorders.
doi.org/10.1097/CM9.0000000000001896
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