PCSK9 inhibition for the treatment of hypercholesterolemia: promises and emerging challenges

Impact of PCSK9 on CTRP9-Induced Metabolic Effects in Adult Rat Cardiomyocytes

The adipocytokine adiponectin and its structural homologs, the C1q/TNF-related proteins (CTRPs), increase insulin sensitivity, fatty acid oxidation and mitochondrial biogenesis. Adiponectin- and CTRP-induced signal transduction has been described to involve the adiponectin receptors and a number of co-receptors including the Low density lipoprotein receptor-related protein 1 (LRP1). LRP1 is another target of the proprotein convertase subtilisin/kexin-9 (PCSK9) in addition to the LDL-receptor (LDL-R). Here, we investigated the influence of PCSK9 on the metabolic effects of CTRP9, the CTRP with the highest homology to adiponectin. Knockdown of LRP1 in H9C2 cardiomyoblasts blunts the effects of CTRP9 on signal transduction and mitochondrial biogenesis, suggesting its involvement in CTRP9-induced cellular effects. Treatment of adult rat cardiomyocytes with recombinant PCSK9 but not knockdown of endogenous PCSK9 by siRNA results in a strong reduction in LRP1 protein expression and subsequently reduces the mitochondrial biogenic effect of CTRP9. PCSK9 treatment (24 h) blunts the effects of CTRP9-induced signaling cascade activation (AMP-dependent protein kinase, protein kinase B). In addition, the stimulating effects of CTRP9 on cardiomyocyte mitochondrial biogenesis and glucose metabolism (GLUT-4 translocation, glucose uptake) are largely blunted. Basal fatty acid (FA) uptake is strongly reduced by exogenous PCSK9, although protein expression of the PCSK9 target CD36, the key regulator of FA transport in cardiomyocytes, is not altered. In addition, only minor effects of PCSK9 were observed on CTRP9-induced FA uptake or the expression of genes involved in FA metabolism or uptake. Finally, this CTRP9-induced increase in CD36 expression occurs independent from LRP1 and LDL-R. In conclusion, PCSK9 treatment influences LRP1-mediated signaling pathways in cardiomyocytes. Thus, therapeutic PCSK9 inhibition may provide an additional benefit through stimulation of glucose metabolism and mitochondrial biogenesis in addition to the known lipid-lowering effects. This could be an important beneficial side effect in situations with impaired mitochondrial function and reduced metabolic flexibility thereby influencing cardiac function.

New Pharmacological Approaches to Target PCSK9

PURPOSE OF REVIEW

Proprotein convertase subtilisin kexin 9 (PCSK9) plays a crucial role in regulating circulating levels of LDL-C as a consequence of its ability to inhibit LDL receptor recycling in the liver. Loss of function variants in the PCSK9 gene result in low LDL-C levels and associate with reduced cardiovascular risk, whereas gain of-function variants associate with hypercholesterolemia and increased risk of early cardiovascular events. Thus, PCSK9 inhibition has been established as an additional approach for the treatment of hypercholesterolemia. The aim of this review is to provide a brief overview of current strategies targeting PCSK9 and discuss clinical results of the emerging approaches.

RECENT FINDINGS

Two monoclonal antibodies targeting circulating PCSK9 (evolocumab and alirocumab) have been approved for the treatment of hypercholesterolemia and cardiovascular disease. Later, a gene silencing approach (inclisiran), which inhibits hepatic PCSK9 synthesis, was shown to be as effective as monoclonal antibodies but with a twice a year injection and is currently under evaluation for approval. Due to the elevated costs of such therapies, several other approaches have been explored, including peptide-based anti PCSK9 vaccination, and small oral PCSK9 inhibitors, which are still in preclinical phase. In the coming years, we will assist to a progressive introduction of novel anti-PCSK9 approaches in the clinical practice for the treatment of patients with hypercholesterolemia as well as patients at high cardiovascular risk.

PCSK9 Inhibition and Atherosclerosis: Current Therapeutic Option and Prospection

Low-density lipoprotein cholesterol (LDL-C) is a pivotal factor in atherosclerotic cardiovascular disease (ASCVD), the leading cause of worldwide mortality. The limitations of statin therapy require alternative treatment strategies to achieve target LDL-C level. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in LDLR recycling, consequently regulating plasma cholesterol levels. Monoclonal antibodies targeting PCSK9 increased expression of LDLRs at the cell surface and therefore decreased circulating LDL-C. PCSK9 inhibitors have shown great efficacy in reducing plasma LDL-C levels, which needs to inject once or twice monthly. Though SPIRE sponsors concern the immunogenicity and terminate trials early, FOURIER and ODYSSER OUTCOME trials improved the efficacy of PCSK9 inhibitors in LDL-C reduction. Inclisiran actually is a small interfering RNA (siRNA) developed to inhibit PCSK9 messenger RNA, leading to reduced concentrations of the PCSK9 protein and thereby lower concentrations of LDL-C. Inclisiran is a latest alternative treatment to cholesterol-lowering therapeutics. Twice injections of inclisiran durably reduced LDL-C levels over 1 year. siRNA therapeutics provided a simple, novel, and less frequent approach to LDL-C reduction in phase I and II trials, which may be used either as in combination with statin therapeutics or a stand-alone therapy in the future.

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Inhibitors, Reality or Dream in Managing Patients with Cardiovascular Disease

BACKGROUND

Statins have been a major keystone in the management of patients with atherosclerotic cardiovascular disease. The benefits of inhibiting HMG CoA reductase, via statins, were translated into reduction in LDL-c with proportionate decrease in cardiovascular events in response to the magnitude of LDL-c reduction. Despite major advances in pharmacological treatments, including the use of high-dose statins, there are urgent need to further reduce future cardiovascular risk. This is in particularly important since 1 out of 5 high-risk atherosclerotic patients who achieve low LDL-c return with a second cardiovascular event within five years. Although this residual risk post-statin is largely heterogeneous, lowering LDL-c beyond 'normal' or guidelines-recommended level using novel therapies has resulted in further reduction in cardiovascular events.

OBJECTIVE

The current review will discuss the use of PCSK9 inhibitors in patients with atherosclerotic disease. PCSK9 inhibitors are a new class of lipid-lowering drugs that are either fully human monoclonal antibodies (evolocumab and alirocumab) or humanised monoclonal antibodies (bococizumab) that effectively reduce LDL-c to unprecedented level. By blocking circulating PCSK9, these drugs would preserve LDL receptors and prevent them from cellular degradation. This process promotes recycling of LDL receptors back to hepatocytes surface, leading into further reduction of LDL-c. Combining PCSK9 inhibitors with statin have led into lower LDL-c, reduction in plaque volume and more importantly reduction in future cardiovascular events.

CONCLUSION

These drugs are very promising, nonetheless, the unselective approach of applying these monoclonal antibodies may not prove to be cost-effective and potentially exposing some patients to unnecessary side effects.

Non-antibody Approaches to Proprotein Convertase Subtilisin Kexin 9 Inhibition: siRNA, Antisense Oligonucleotides, Adnectins, Vaccination, and New Attempts at Small-Molecule Inhibitors Based on New Discoveries

Low-density lipoprotein (LDL) is one of the principal risk factors for atherosclerosis. Circulating LDL particles can penetrate into the sub-endothelial space of arterial walls. These particles undergo oxidation and promote an inflammatory response, resulting in injury to the vascular endothelial wall. Persistent elevation of LDL-cholesterol (LDL-C) is linked to the progression of fatty streaks to lipid-rich plaque and thus atherosclerosis. LDL-C is a causal factor for atherosclerotic cardiovascular disease and lowering it is beneficial across a range of conditions associated with high risk of cardiovascular events. Therefore, all guidelines-recommended initiations of statin therapy for patients at high cardiovascular risk is irrespective of LDL-C. In addition, intensive LDL-C lowering therapy with statins has been demonstrated to result in a greater reduction of cardiovascular event risk in large clinical trials. However, many high-risk patients receiving statins fail to achieve the guideline-recommended reduction in LDL-C levels in routine clinical practice. Moreover, low levels of adherence and often high rates of discontinuation demand the need for further therapies. Ezetimibe has typically been used as a complement to statins when further LDL-C reduction is required. More recently, proprotein convertase subtilisin kexin 9 (PCSK9) has emerged as a novel therapeutic target for lowering LDL-C levels, with PCSK9 inhibitors offering greater reductions than feasible through the addition of ezetimibe. PCSK9 monoclonal antibodies have been shown to not only considerably lower LDL-C levels but also cardiovascular events. However, PCSK9 monoclonal antibodies require once- or twice-monthly subcutaneous injections. Further, their manufacturing process is expensive, increasing the cost of therapy. Therefore, several non-antibody treatments to inhibit PCSK9 function are being developed as alternative approaches to monoclonal antibodies. These include gene-silencing or editing technologies, such as antisense oligonucleotides, small interfering RNA, and the clustered regularly interspaced short palindromic repeats/Cas9 platform; small-molecule inhibitors; mimetic peptides; adnectins; and vaccination. In this review, we summarize the current knowledge base on the role of PCSK9 in lipid metabolism and an overview of non-antibody approaches for PCSK9 inhibition and their limitations. The subsequent development of alternative approaches to PCSK9 inhibition may give us more affordable and convenient therapeutic options for the management of high-risk patients.

The Pharmacologic Role and Clinical Utility of PCSK9 Inhibitors for the Treatment of Hypercholesterolemia

In addition to monoclonal antibodies against proprotein convertase subtilisin-kexin type 9 (PCSK9), vaccines against PCSK9 and smaller molecule inhibitors as well as RNA inhibitors of PCSK9 production have been created. The monoclonal antibodies against PCSK9 and the PCSK9 RNA inhibitors can reduce low-density lipoproteins (LDLs) by over 50%, non-high-density lipoprotein (HDL) cholesterol and triglycerides, and increasing HDL. Although effective in several homozygous familial hypercholesterolemia patient types, PCSK9 inhibitors does not work in all patient types. Outcome trials show no effects on mortality but do show reductions in atherosclerotic events such as myocardial infarctions, strokes, and need for coronary revascularization. PCSK9 inhibitors have a very attractive safety profile with no significant elevations in measures of muscle or liver damage. The current and more advanced experimental agents all require subcutaneous dosing, and injection site reactions are among the most common adverse events. Therapy for the Food and Drug Administration (FDA) approved agents is markedly expensive, and this is the primary barrier to utilization. However, it is possible to identify patients with a number needed to treat to prevent an atherosclerotic event low enough to render it cost-effective and one such factor is whether or not you require a 50% reduction in LDL in order to achieve your LDL goal.

Cardiovascular Outcomes of PCSK9 Inhibitors: With Special Emphasis on Its Effect beyond LDL-Cholesterol Lowering

PCSK9 inhibitors, monoclonal antibodies, are novel antihypercholesterolemic drugs. FDA first approved them in July 2015. PCSK9 protein (692-amino acids) was discovered in 2003. It plays a major role in LDL receptor degradation and is a prominent modulator in low-density lipoprotein cholesterol (LDL-C) metabolism. PCSK9 inhibitors are monoclonal antibodies that target PCSK9 protein in liver and inhibiting this protein leads to drastically lowering harmful LDL-C level in the bloodstream. Despite widespread use of the statin, not all the high-risk patients were able to achieve targeted level of LDL-C. Using PCSK9 inhibitors could lead to a substantial decrement in LDL-C plasma level ranging from 50% to 70%, either as a monotherapy or on top of statins. A large number of trials have shown robust reduction of LDL-C plasma level with the use of PCSK9 inhibitors as a monotherapy or in combination with statins in familial and nonfamilial forms of hypercholesterolemia. Moreover, PCSK9 inhibitors do not appear to increase the risk of hepatic and muscle-related side effects. PCSK9 inhibitors proved to be a highly potent and promising antihypercholesterolemic drug by decreasing LDL-R lysosomal degradation by PCSK9 protein. Statin drugs are known to have some pleiotropic effects. In this article, we are also focusing on the effects of PCSK9 inhibitor beyond LDL-C reduction like endothelial inflammation, atherosclerosis, its safety in patients with diabetes, obesity, and chronic kidney disease, and its influence on neurocognition and stroke.

Proprotein Convertase Subtilisin-Kexin type-9 (PCSK9) and triglyceride-rich lipoprotein metabolism: Facts and gaps

After more than a decade of intense investigation, Pro-protein Convertase Subtilisin-Kexin type 9 (PCSK9) remains a hot topic of research both at experimental and clinical level. Interestingly PCSK9 is expressed in different tissues suggesting the existence of additional function(s) beyond the modulation of the Low-Density Lipoprotein (LDL) receptor in the liver. Emerging data suggest that PCSK9 might play a role in the modulation of triglyceride-rich lipoprotein (TGRL) metabolism, mainly Very Low-Density Lipoproteins (VLDL) and their remnants. In vitro, PCSK9 affects TGRLs production by intestinal cells as well as the catabolism of LDL receptor homologous and non-homologous targets such as VLDL receptor, CD36 and ApoE2R. However, the in vivo relevance of these findings is still debated. This review aims at critically discussing the role of PCSK9 on TGRLs metabolism with a major focus on the impact of its genetic and pharmacological modulation on circulating lipids and lipoproteins beyond LDL.

Future Lipid-Altering Therapeutic Options Targeting Residual Cardiovascular Risk

Low-density lipoproteins (LDL) play a causal role in the development of atherosclerosis, and reduction of LDL cholesterol with a statin is a cornerstone in prevention of cardiovascular disease. However, it remains an unmet need to reduce the residual risk on maximally tolerated statin alone or in combination with other drugs such as ezetimibe. Among the new LDL-lowering therapies, PCSK9 inhibitors appear the most promising class. Genetic studies suggest that triglyceride-rich lipoproteins are associated with cardiovascular risk and several promising triglyceride-lowering therapies are at various stages of development. At the opposite end, high-density lipoprotein (HDL) cholesterol seems to not be causally associated with cardiovascular risk, and thus far, trials designed to reduce cardiovascular risk by mainly raising HDL cholesterol levels have been disappointing. Nevertheless, new drugs targeting HDL are still in development. This review describes the new drugs reducing LDL, apolipoprotein(a), and triglyceride-rich lipoproteins, and the strategies to modulate HDL metabolism.

Anti-PCSK9 antibodies for the treatment of heterozygous familial hypercholesterolemia: patient selection and perspectives

Heterozygous familial hypercholesterolemia (FH) is a genetic disorder characterized by high low-density lipoprotein cholesterol levels from birth, which exposes the arteries to high levels of atherogenic lipoproteins lifelong and results in a significantly increased risk of premature cardiovascular events. The diagnosis of FH, followed by an appropriate and early treatment is critical to reduce the cardiovascular burden in this population. Phase I–III clinical trials showed the benefit of proprotein convertase subtilisin kexin 9 inhibitors, both alirocumab and evolocumab, in these patients with an average low-density lipoprotein cholesterol reduction ranging from −40% to −60%. The aim of this review is to address the unmet needs in cholesterol management, elucidate the biology and the clinical benefit of proprotein convertase subtilisin kexin 9 inhibition and finally discuss the open gaps and future directions in the treatment of patients with heterozygous FH.

Proprotein convertase subtilisin kexin type 9 inhibitors: update from clinical trials to real-world experience

PURPOSE OF REVIEW

After the approval of alirocumab and evolocumab, the first two monoclonal antibodies (mAbs) targeting proprotein convertase subtilisin kexin type 9 (PCSK9), this review provides an update on recent PCSK9 inhibitors data and describes recommendations for the use before the results of the ongoing cardiovascular endpoint trials.

RECENT FINDINGS

New studies and complementary analysis of phase III trials have consistently shown that alirocumab and evolocumab are highly effective in reducing LDL-cholesterol and to some extent lipoprotein (a). Some preliminary findings coming from exploratory and post-hoc analyses of the longer-term safety phase III trials and meta-analyses suggest that these mAbs can decrease the incidence of cardiovascular events. Whether or not mAbs targeting PCSK9 definitively reduce the incidence of cardiovascular events without safety concerns shall be demonstrated with the ongoing cardiovascular outcome trials. Waiting these outcome trials and given the high cost of these mAbs, groups of experts have proposed as priorities groups of patients with familial hypercholesterolemia and with atherosclerotic cardiovascular disease who have substantially elevated LDL-cholesterol on maximally tolerated statin/ezetimibe therapy.

SUMMARY

Before the results of large cardiovascular outcome trials, PCSK9 inhibitors should be only used in some categories of patients with familial hypercholesterolemia and/or with atherosclerotic cardiovascular disease.

Impact of diet and exercise on proprotein convertase subtilisin/kexin 9: A mini-review

Proprotein Convertase Subtilisin/Kexin 9 (PCSK9) plays an important role in the regulation of blood cholesterol levels, and inhibition of PCSK9 with monoclonal antibodies reduces LDL cholesterol by more than 50% over and above what can be achieved with statins or ezetimibe alone. Diet and exercise influence PCSK9 levels; however data on this issue are scarce. Regarding diet, a high oleic canola/docosahexaenoic acid oil blend, marine n-3 polyunsaturated fatty acids, vegetable n-6 polyunsaturated fatty acids, a Mediterranean style diet and acute fasting, but not necessarily weight reduction are associated with low PCSK9 concentrations, whereas a high fructose diet is associated with high PCSK9 concentrations. Animal data regarding the effect of diet on PCSK9 must be interpreted with caution, because even between rodent species, significant differences become apparent. Regarding exercise, a decrease in PCSK9 has been reported in one investigation along with an intervention promoting active use of stairs rather than elevators. Reports from sparse animal studies regarding the effect of exercise on PCSK9 have yielded varying results.

Management of Hypercholesterolemia, Appropriateness of Therapeutic Approaches and New Drugs in Patients with High Cardiovascular Risk

Control of lipid levels is one of the most effective strategies for cardiovascular (CV) event prevention. In fact, many clinical trials have clearly demonstrated that low-density lipoprotein cholesterol (LDL-C) lowering, primarily with statins, reduces major CV events and mortality. The evidence from these trials has been useful in designing the cholesterol treatment guidelines, which are mainly aimed at preventing and managing cardiovascular disease (CVD). However, available data indicate that a large proportion of patients fail to achieve lipid goals, and this is particularly frequent in patients at high or very high CV risk. Furthermore, owing to side effects, a significant percentage of patients cannot tolerate statin treatment. Hence, researchers have focused their attention on novel LDL-C-lowering agents that act via mechanisms distinct from that of statins. Among the new compounds under investigation, the monoclonal antibodies to proprotein convertase subtilisin/kexin type 9 (PCSK9) seem particularly promising, having recently been shown to be well tolerated and highly effective at lowering LDL-C, with a possible effect on the occurrence of CV events. Currently, alirocumab is approved by the US Food and Drug Administration (FDA) as an adjunct to diet and maximally tolerated statin therapy for use in adults with heterozygous familial hypercholesterolemia (FH) or those with atherosclerotic CV disease who require additional LDL-C lowering; it has also been recently approved by the European Medicines Agency (EMA) for use in patients with heterozygous FH, non–familial hypercholesterolemia or mixed dyslipidemia in whom statins are ineffective or not tolerated. Evolocumab is approved by the FDA as an adjunct to diet and maximally tolerated statins for adults with hetero- and homozygous FH and those with atherosclerotic CV disease who require additional lowering of LDL-C, and by the EMA in adults with primary hypercholesterolemia or mixed dyslipidemia, as an adjunct to diet, in combination with a statin or a statin with other lipid lowering therapies in patients unable to reach LDL-C goals with the maximum tolerated dose of a statin; alone or in combination with other lipid lowering therapies in patients who are statin-intolerant, or those for whom a statin is contraindicated. Evolocumab is also indicated in adults and adolescents aged 12 years and over with homozygous familial hypercholesterolemia in combination with other lipid-lowering therapies.

Biology of proprotein convertase subtilisin kexin 9: beyond low-density lipoprotein cholesterol lowering

Proprotein convertase subtilisin kexin 9 (PCSK9) is a key regulator of low-density lipoprotein receptor levels and LDL-cholesterol levels. Loss-of-function mutations in PCSK9 gene are associated with hypocholesterolaemia and protection against cardiovascular disease, identifying PCSK9 inhibition as a valid therapeutic approach to manage hypercholesterolaemia and related diseases. Although PCSK9 is expressed mainly in the liver, it is present also in other tissues and organs with specific functions, raising the question of whether a pharmacological inhibition of PCSK9 to treat hypercholesterolaemia and associated cardiovascular diseases might be helpful or deleterious in non-hepatic tissues. For example, PCSK9 is expressed in the vascular wall, in the kidneys, and in the brain, where it was proposed to play a role in development, neurocognitive process, and neuronal apoptosis. A link between PCSK9 and immunity was also proposed as both sepsis and viral infections are differentially affected in the presence or absence of PCSK9. Despite the increasing number of observations, the debate on the exact roles of PCSK9 in extrahepatic tissues is still ongoing, and as very effective drugs that inhibit PCSK9 have become available to the clinician, a better understanding of the biological roles of PCSK9 is warranted.

Role of Brown Fat in Lipoprotein Metabolism and Atherosclerosis

Atherosclerosis, for which hyperlipidemia is a major risk factor, is the leading cause of morbidity and mortality in Western society, and new therapeutic strategies are highly warranted. Brown adipose tissue (BAT) is metabolically active in human adults. Although positron emission tomography-computed tomography using a glucose tracer is the golden standard to visualize and quantify the volume and activity of BAT, it has become clear that activated BAT combusts fatty acids rather than glucose. Here, we review the role of brown and beige adipocytes in lipoprotein metabolism and atherosclerosis, with evidence derived from both animal and human studies. On the basis of mainly data from animal models, we propose a model in which activated brown adipocytes use their intracellular triglyceride stores to generate fatty acids for combustion. BAT rapidly replenishes these stores by internalizing primarily lipoprotein triglyceride-derived fatty acids, generated by lipoprotein lipase-mediated hydrolysis of triglycerides, rather than by holoparticle uptake. As a consequence, BAT activation leads to the generation of lipoprotein remnants that are subsequently cleared via the liver provided that an intact apoE-low-density lipoprotein receptor pathway is present. Through these mechanisms, BAT activation reduces plasma triglyceride and cholesterol levels and attenuates diet-induced atherosclerosis development. Initial studies suggest that BAT activation in humans may also reduce triglyceride and cholesterol levels, but potential antiatherogenic effects should be assessed in future studies.

Current Treatment of Dyslipidemia: Evolving Roles of Non-Statin and Newer Drugs

Since their introduction, statin (HMG-CoA reductase inhibitor) drugs have advanced the practice of cardiology to unparalleled levels. Even so, coronary heart disease (CHD) still remains the leading cause of death in developed countries, and is predicted to soon dominate the causes of global mortality and disability as well. The currently available non-statin drugs have had limited success in reversing the burden of heart disease, but new information suggests they have roles in sizeable subpopulations of those affected. In this review, the status of approved non-statin drugs and the significant potential of newer drugs are discussed. Several different ways to raise plasma high-density lipoprotein (HDL) cholesterol (HDL-C) levels have been proposed, but disappointments are now in large part attributed to a preoccupation with HDL quantity, rather than quality, which is more important in cardiovascular (CV) protection. Niacin, an old drug with many antiatherogenic properties, was re-evaluated in two imperfect randomized controlled trials (RCTs), and failed to demonstrate clear effectiveness or safety. Fibrates, also with an attractive antiatherosclerotic profile and classically used for hypertriglyceridemia, lacks evidence-based proof of efficacy, save for a subgroup of diabetic patients with atherogenic dyslipidemia. Omega-3 fatty acids fall into this category as well, even with an impressive epidemiological evidence base. Omega-3 research has been plagued with methodological difficulties yielding tepid, uncertain, and conflicting results; well-designed studies over longer periods of time are needed. Addition of ezetimibe to statin therapy has now been shown to decrease levels of low-density lipoprotein (LDL) cholesterol (LDL-C), accompanied by a modest decrease in the number of CV events, though without any improvement in CV mortality. Importantly, the latest data provide crucial evidence that LDL lowering is central to the management of CV disease. Of drugs that inhibit cholesteryl ester transfer protein (CETP) tested thus far, two have failed and two remain under investigation and may yet prove to be valuable therapeutic agents. Monoclonal antibodies to proprotein convertase subtilisin/kexin type 9, now in phase III trials, lower LDL-C by over 50 % and are most promising. These drugs offer new ability to lower LDL-C in patients in whom statin drug use is, for one reason or another, limited or insufficient. Mipomersen and lomitapide have been approved for use in patients with familial hypercholesterolemia, a more common disease than appreciated. Anti-inflammatory drugs are finally receiving due attention in trials to elucidate potential clinical usefulness. All told, even though statins remain the standard of care, non-statin drugs are poised to assume a new, vital role in managing dyslipidemia.

Defining the Role of PCSK9 Inhibitors in the Treatment of Hyperlipidemia

Statins remain the mainstay of medical cardiovascular risk reduction because of their effectiveness in decreasing low-density lipoprotein cholesterol (LDL-C) as well as some other potentially beneficial effects. The latest US 2013 lipid guidelines essentially recommend only the prescription of a high-dose statin for the high-risk patient. However, both quite old and quite new outcomes evidence, such as reported for ezetimibe, emphasize that LDL-C lowering is, in and of itself, quite important for cardiovascular risk reduction. It appears that the proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors represent a major new contribution to this effort, especially for patients with severe familial hypercholesterolemia, proven clinical cardiovascular disease, statin intolerance, or failure to attain an acceptably low LDL-C goal despite maximum available medical management. Very recent clinical trials have proven overwhelmingly the effectiveness and safety of PCSK9 inhibitors for lowering LDL-C. Both alirocumab and evolocumab have now been approved by the US FDA and there are some initial favorable outcomes data. This review is intended to summarize available evidence and emphasize the possible clinical role of these inhibitors following the approval of alirocumab and evolocumab. Understanding the negative receptor feedback of PCSK9 and the mechanism and beneficial effect of PCSK9 inhibitors for cardiovascular risk reduction is essential for the up-to-date practitioner of cardiovascular medicine. There is every reasonable hope for significant cardiovascular benefit from these new additions to our medical cardiovascular armamentarium.

Antilipidemic Drug Therapy Today and in the Future

The armamentarium for the treatment of dyslipidemia today comprises six different modes of action with overall around 24 different drugs. The treatment of lipid disorders was revolutionized with the introduction of statins which have become the most important therapeutic option available today to reduce and prevent atherosclerosis and its detrimental consequences like cardiovascular diseases and stroke. With and optimized reduction of elevated LDL levels with statins, the risk for cardiovascular diseases (CVD) can be reduced by 30%, indicating a residual remaining risk of 70% for the development and progression of CVD notifying still a high medical need for more effective antilipidemic drugs. Consequently, the search for novel lipid-modifying drugs is still one of the most active areas in research and development in the pharmaceutical industry. Major focus lies on approaches to LDL-lowering drugs superior to statins with regard to efficacy, safety, and patient compliance and on approaches modifying plasma levels and functionality of HDL particles based on the clinically validated inverse relationship between high-plasma HDL levels and the risk for CVD. The available drugs today for the treatment of dyslipidemia are small organic molecules or nonabsorbable polymers for binding of bile acids to be applied orally. Besides small molecules for novel targets, biological drugs such as monoclonal antibodies, antisense or gene-silencing oligonucleotides, peptidomimetics, reconstituted synthetic HDL particles and therapeutic proteins are novel approaches in clinical development are which have to be applied by injection or infusion. The promising clinical results of several novel drug candidates, particularly for LDL cholesterol lowering with monoclonal antibodies raised against PCSK9, may indicate more than a decade after the statins, the entrance of new breakthrough therapies to treat lipid disorders.

Therapeutic Potential and Critical Analysis of the PCSK9 Monoclonal Antibodies Evolocumab and Alirocumab

OBJECTIVE

To review the mechanism of action for PCSK9 monoclonal antibodies and critically evaluate the therapeutic potential of evolocumab and alirocumab in the treatment of hypercholesterolemia.

DATA SOURCES

Ovid MEDLINE search from 1980 to August 2015 using the terms PCSK9, evolocumab, and alirocumab with forward and backward citation tracking.

STUDY SELECTION AND DATA EXTRACTION

English-language trials and studies assessing the mechanism, efficacy, or safety of PCSK9 monoclonal antibodies were included.

DATA SYNTHESIS

PCSK9 monoclonal antibodies have a potent ability to reduce low-density lipoprotein (LDL) by almost 50% in controlled trials: -47.49% (95% CI = -69.6% to -25.4%). They have an acceptable safety profile with no significant elevations in Creatine Kinase (CK) (odds ratio [OR] = 0.72; 95% CI = 0.54 to 0.96) or serious adverse events (OR = 1.01; 95% CI = 0.87 to 1.18), and preliminary evidence suggests reductions in myocardial infarction (OR = 0.49; 95% CI = 0.26 to 0.93). Although it is effective in several familial hypercholesterolemia (FH) patient types, it does not work in homozygous patients with dual allele LDL receptor negative polymorphisms or those who are homozygous for autosomal recessive hypercholesterolemia.

CONCLUSIONS

Although not preferred over statins because of limited clinical trial evidence of cardiovascular event reductions, dosing convenience, and expense, PCSK9 monoclonal antibodies will have a prominent role to play in the treatment of hypercholesterolemia, especially in patients needing large LDL reductions, including patients with many types of FH.

Marine n-3 polyunsaturated fatty acids lower plasma proprotein convertase subtilisin kexin type 9 levels in pre- and postmenopausal women: A randomised study

OBJECTIVE

To investigate whether a supplement of 2.2g of marine n-3 polyunsaturated fatty acids (PUFA) influences plasma proprotein convertase subtilisin kexin type 9 (PCSK9) levels in pre- and postmenopausal women.

METHODS

Ninety-two healthy women were randomly assigned to consume 2.2g marine n-3 PUFA or a control oil (thistle oil) daily for 12 weeks. Adipose tissue, a long-term marker of dietary intake of seafood was collected at baseline and blood samples were drawn at baseline and after 12 weeks of supplement intake.

RESULTS

Plasma PCSK9 levels were significantly reduced by 11.4% for premenopausal women and 9.8% for postmenopausal women after the supplement of 2.2g of marine n-3 PUFA compared with control oil. The mean change of plasma PCSK9 levels between participants receiving marine n-3 PUFA and control oil was 16.1% for premenopausal women and 13.1% for postmenopausal women. There was, however, no correlation between baseline levels of plasma PCSK9 and the fatty acid content of marine n-3 PUFA in adipose tissue.

CONCLUSION

This study showed that 2.2g marine n-3 PUFA reduce plasma PCSK9 levels in both pre- and postmenopausal women.

PCSK9 R46L, lower LDL, and cardiovascular disease risk in familial hypercholesterolemia: a cross-sectional cohort study

OBJECTIVE

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a downregulator of the low density lipoprotein receptor. The aims of this cross-sectional cohort-study were to examine whether the PCSK9 R46L loss of function variant found in a cohort of familial hypercholesterolemia (FH) patients was associated with lower low density lipoprotein cholesterol, lower frequency of xanthomata, and cardiovascular risk.

APPROACH AND RESULTS

We studied FH patients attending the IRCM (Institut de Recherches Cliniques de Montréal) Lipid Clinic and whose DNA genotyping was positive for a low density lipoprotein receptor mutation. The presence of the PCSK9 loss of function R46L missense variant was determined among a cohort of 582 FH patients by genotyping. Frequency of the R46L variant was 3%. Carriers had significantly lower low density lipoprotein cholesterol (11%, P=0.002), total cholesterol (9%, P=0.007), apolipoprotein B (10%, P=0.037), and non-high density lipoprotein (12%, P<0.001) concentrations compared with noncarriers. Furthermore, R46L carriers showed a decreased average number of xanthoma per individual compared with noncarriers (0.33 and 0.76, respectively; P<0.001). Importantly, the R46L genetic variant was associated with a significant 86% lower odd of presenting a cardiovascular event (odds ratio, 0.14; 95% confidence interval, 0.032-0.63; P=0.001).

CONCLUSIONS

Even though the R46L variant was present in 3% of our FH population, carriers of this polymorphism showed attenuated effect of the low density lipoprotein receptor mutation on parameters, such as low density lipoprotein cholesterol, apolipoprotein B, total cholesterol, and non-high density lipoprotein. More importantly, this mutation is associated with a significant lower risk of cardiovascular disease compared with noncarriers. It is therefore likely that targeting PCSK9 in FH patients with novel anti-PCSK9 therapies will be useful in reducing cardiovascular risk in affected subjects.