Antisense oligonucleotides for the treatment of dyslipidaemia.

Antisense oligonucleotides (ASOs) are short synthetic analogues of natural nucleic acids designed to specifically bind to a target messenger RNA (mRNA) by Watson-Crick hybridization, inducing selective degradation of the mRNA or prohibiting translation of the selected mRNA into protein. Antisense technology has the ability to inhibit unique targets with high specificity and can be used to inhibit synthesis of a wide range of proteins that could influence lipoprotein levels and other targets. A number of different classes of antisense agents are under development. To date, mipomersen, a 2'-O-methoxyethyl phosphorothioate 20-mer ASO, is the most advanced ASO in clinical development. It is a second-generation ASO developed to inhibit the synthesis of apolipoprotein B (apoB)-100 in the liver. In Phase 3 clinical trials, mipomersen has been shown to significantly reduce plasma low-density lipoprotein cholesterol (LDL-c) as well as other atherogenic apoB containing lipoproteins such as lipoprotein (a) [Lp(a)] and small-dense LDL particles. Although concerns have been raised because of an increase in intrahepatic triglyceride content, preliminary data from long-term studies suggest that with continued treatment, liver fat levels tend to stabilize or decline. Further studies are needed to evaluate potential clinical relevance of these changes. Proprotein convertase subtilisin/kexin-9 (PCSK9) is another promising novel target for lowering LDL-c by ASOs. Both second-generation ASOs and ASOs using locked nucleic acid technology have been developed to inhibit PCSK9 and are under clinical development. Other targets currently being addressed include apoC-III and apo(a) or Lp(a). By directly inhibiting the synthesis of specific proteins, ASO technology offers a promising new approach to influence the metabolism of lipids and to control lipoprotein levels. Its application to a wide variety of potential targets can be expected if these agents prove to be clinically safe and effective.

Mipomersen, an apolipoprotein B synthesis inhibitor, lowers low-density lipoprotein cholesterol in high-risk statin-intolerant patients: a randomized, double-blind, placebo-controlled trial.

AIMS: A randomized, double-blind, placebo-controlled study was conducted to investigate the safety and efficacy of mipomersen, an apolipoprotein B-100 (apoB) synthesis inhibitor, in patients who are statin intolerant and at high risk for cardiovascular disease (CVD). METHODS AND RESULTS: Thirty-three subjects, not receiving statin therapy because of statin intolerance, received a weekly subcutaneous dose of 200 mg mipomersen or placebo (2:1 randomization) for 26 weeks. The primary endpoint was per cent change in LDL cholesterol (LDL-c) from the baseline to Week 28. The other efficacy endpoints were per cent change in apoB and lipoprotein a [Lp(a)]. Safety was determined using the incidence of treatment-emergent adverse events (AEs) and clinical laboratory evaluations. After 26 weeks of mipomersen administration, LDL-c was reduced by 47 ± 18% (P < 0.001 vs. placebo). apoB and Lp(a) were also significantly reduced by 46 and 27%, respectively (P < 0.001 vs. placebo). Four mipomersen (19%) and two placebo subjects (17%) discontinued dosing prematurely due to AEs. Persistent liver transaminase increases ≥ 3× the upper limit of normal were observed in seven (33%) subjects assigned to mipomersen. In selected subjects, liver fat content was assessed, during and after treatment, using magnetic resonance spectroscopy. Liver fat content in these patients ranged from 0.8 to 47.3%. Liver needle biopsy was performed in two of these subjects, confirming hepatic steatosis with minimal inflammation or fibrosis. CONCLUSION: The present data suggest that mipomersen is a potential therapeutic option in statin-intolerant patients at high risk for CVD. The long-term follow-up of liver safety is required. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00707746.

An increased burden of common and rare lipid-associated risk alleles contributes to the phenotypic spectrum of hypertriglyceridemia.

OBJECTIVE: Earlier studies have suggested that a common genetic architecture underlies the clinically heterogeneous polygenic Fredrickson hyperlipoproteinemia (HLP) phenotypes defined by hypertriglyceridemia (HTG). Here, we comprehensively analyzed 504 HLP-HTG patients and 1213 normotriglyceridemic controls and confirmed that a spectrum of common and rare lipid-associated variants underlies this heterogeneity. METHODS AND RESULTS: First, we demonstrated that genetic determinants of plasma lipids and lipoproteins, including common variants associated with plasma triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) from the Global Lipids Genetics Consortium were associated with multiple HLP-HTG phenotypes. Second, we demonstrated that weighted risk scores composed of common TG-associated variants were distinctly increased across all HLP-HTG phenotypes compared with controls; weighted HDL-C and LDL-C risk scores were also increased, although to a less pronounced degree with some HLP-HTG phenotypes. Interestingly, decomposition of HDL-C and LDL-C risk scores revealed that pleiotropic variants (those jointly associated with TG) accounted for the greatest difference in HDL-C and LDL-C risk scores. The APOE E2/E2 genotype was significantly overrepresented in HLP type 3 versus other phenotypes. Finally, rare variants in 4 genes accumulated equally across HLP-HTG phenotypes. CONCLUSIONS: HTG susceptibility and phenotypic heterogeneity are both influenced by accumulation of common and rare TG-associated variants.

Excess of rare variants in genes identified by genome-wide association study of hypertriglyceridemia.

Genome-wide association studies (GWAS) have identified multiple loci associated with plasma lipid concentrations. Common variants at these loci together explain <10% of variation in each lipid trait. Rare variants with large individual effects may also contribute to the heritability of lipid traits; however, the extent to which rare variants affect lipid phenotypes remains to be determined. Here we show an accumulation of rare variants, or a mutation skew, in GWAS-identified genes in individuals with hypertriglyceridemia (HTG). Through GWAS, we identified common variants in APOA5, GCKR, LPL and APOB associated with HTG. Resequencing of these genes revealed a significant burden of 154 rare missense or nonsense variants in 438 individuals with HTG, compared to 53 variants in 327 controls (P = 6.2 x 10(-8)), corresponding to a carrier frequency of 28.1% of affected individuals and 15.3% of controls (P = 2.6 x 10(-5)). Considering rare variants in these genes incrementally increased the proportion of genetic variation contributing to HTG.

Apolipoprotein B synthesis inhibition: results from clinical trials.

PURPOSE OF REVIEW: Mipomersen is a second-generation antisense oligonucleotide developed to inhibit the synthesis of apolipoprotein B-100 in the liver. In this review we will summarize the results of recent preclinical and clinical studies addressing safety and low-density lipoprotein-cholesterol (LDL-c) lowering efficacy of this new compound. RECENT FINDINGS: In phase 3 clinical trials, mipomersen has been shown to significantly reduce LDL-c in patients with homozygous and heterozygous familial hypercholesterolemia on maximally tolerated lipid-lowering therapy. Injection site reactions, flu-like symptoms and increases in liver transaminases were the main adverse events. A recent safety study, designed to investigate the effects of mipomersen on intrahepatic triglyceride content, failed to show evidence of clinically relevant hepatic steatosis after 13 weeks of treatment. SUMMARY: Mipomersen is a new agent to lower LDL-c in patients at increased risk of cardiovascular disease and/or intolerant to statins. Whereas safety concerns have focused on hepatic fat accumulation, to date no evidence of clinically relevant increases of intrahepatic triglyceride content are reported. Ongoing and future studies are eagerly awaited to assess the impact of mipomersen on hepatic triglyceride content after prolonged exposure.

Effect of mipomersen, an apolipoprotein B synthesis inhibitor, on low-density lipoprotein cholesterol in patients with familial hypercholesterolemia.

A randomized, double-blind, placebo-controlled, dose-escalation study was conducted to examine the efficacy and safety of mipomersen (ISIS 301012), an antisense inhibitor of apolipoprotein B, when added to conventional lipid-lowering therapy for patients with heterozygous familial hypercholesterolemia. A total of 44 patients were enrolled and were separated into 4 cohorts, with doses ranging from 50 to 300 mg (4:1 active treatment/placebo ratio). Patients received 8 doses subcutaneously during a 6-week treatment period. Patients assigned to the 300-mg dose continued for an additional 7 weeks with once-per-week dosing. The primary efficacy end point was the percentage of change from baseline to week 7 in low-density lipoprotein (LDL) cholesterol. Safety was assessed using the laboratory test results and according to the incidence, severity, and relation of adverse events to drug dose. Mipomersen produced significant reductions in LDL cholesterol and other atherogenic apolipoprotein B-containing lipoproteins. After 6 weeks of treatment, the LDL cholesterol level was reduced by 21% from baseline in the 200-mg/week dose group (p <0.05) and 34% from baseline in the 300-mg/week dose group (p <0.01), with a concomitant reduction in apolipoprotein B of 23% (p <0.05) and 33% (p <0.01), respectively. Injection site reactions were the most common adverse event. Elevations in liver transaminase levels (> or =3 times the upper limit of normal) occurred in 4 (11%) of 36 patients assigned to active treatment; 3 of these patients were in the highest dose group. In conclusion, mipomersen has an incremental LDL cholesterol lowering effect when added to conventional lipid-lowering therapy.

The metabolism of triglyceride-rich lipoproteins revisited: new players, new insight.

Peripheral lipoprotein lipase (LPL)-mediated lipolysis of triglycerides is the first step in chylomicron/VLDL clearance involving heparan sulfate proteoglycans (HSPGs) displayed at the cell surface of the capillaries in adipose tissue, heart and skeletal muscle. The newly generated chylomicron remnant particles are then cleared by the liver, whereas VLDL remnant particles are either further modified, through the action of hepatic lipase (HL) and cholesteryl ester transfer protein (CETP), into LDL particles or alternatively directly cleared by the liver. Two proteins, lipase maturation factor 1 (LMF1) and glycosylphosphatidylinositol-anchored high density lipoprotein binding protein 1 (GPIHBP1), have been recently identified and have revised our current understanding of LPL maturation and LPL-mediated lipolysis. Moreover, new insights have been gained with respect to hepatic remnant clearance using genetically modified mice targeting the sulfation of HSPGs and even deletion of the most abundant heparan sulfate proteoglycan: syndecan1. In this review, we will provide an overview of novel data on both peripheral TG hydrolysis and hepatic remnant clearance that will improve our knowledge of plasma triglyceride metabolism.

Effect of apolipoprotein-B synthesis inhibition on liver triglyceride content in patients with familial hypercholesterolemia.

To investigate the impact of mipomersen, an apolipoprotein B-100 (apoB) synthesis inhibitor, on intra-hepatic triglyceride content (IHTG content), we conducted a randomized, double-blind, placebo-controlled study in 21 patients with familial hypercholesterolemia (FH). Subjects received a weekly subcutaneous dose of 200 mg mipomersen or placebo for 13 weeks while continuing conventional lipid lowering therapy. The primary endpoint was change in IHTG content from week 0 to week 15 as measured by localized proton magnetic resonance spectroscopy (1H-MRS). Thirteen weeks of mipomersen administration reduced LDL-cholesterol by 22.0 (17.8) % and apoB by 19.9 (17.4) % (both P < 0.01). One of 10 patients (10%) in the mipomersen-treated group developed mild hepatic steatosis at week 15, which was reversible following mipomersen discontinuation. For the group, there was a trend toward an increase in IHTG content [placebo; baseline: 1.2% and week 15: 1.1%; change -0.1 (0.9). Mipomersen; baseline: 1.2% and week 15: 2.1%; change 0.8 (1.7) (P = 0.0513)]. Mipomersen administration for 13 weeks to subjects with FH is associated with a trend toward an increase in IHTG content. Future studies evaluating the effects of long-term use of mipomersen reaching more profound reductions in apoB are required prior to broader use of this compound.

Metabolic dyslipidemia and risk of future coronary heart disease in apparently healthy men and women: the EPIC-Norfolk prospective population study.

BACKGROUND: The association of metabolic syndrome and risk of CHD is now well established. The association between 'metabolic dyslipidemia' as defined by high triglycerides (TG) and low high-density lipoprotein cholesterol (HDL-C) levels and the risk of coronary heart disease (CHD) risk is not known. The aim of this study was to investigate the association between metabolic dyslipidemia, and risk of coronary heart disease (CHD) in apparently healthy men and women. METHODS: Metabolic dyslipidemia was defined by combination of increased triglyceride (TG) levels (≥150 mg/dl) and low high-density lipoprotein cholesterol (HDL-C) levels (≤50 mg/dl for women and ≤40 mg/dl for men). In the EPIC-Norfolk prospective population study, 21,340 participants without diabetes (9326 men and 12,014 women) were followed for a mean of 11.4 years during which 2075 CHD events occurred. Three multivariate models were used adjusting for other metabolic risk factors including low-density lipoprotein cholesterol (LDL-C). RESULTS: Compared to men with normal HDL and normal TG, men with metabolic dyslipidemia had an increased risk for CHD (HR 1.61, 95% CI 1.40-1.86). The increased risk remained significant after adjustment for LDL-C and other metabolic risk factors. Among women, metabolic dyslipidemia was associated with increased CHD risk (HR 1.78, 95% CI 1.47-2.15). This association was lost when the model was additionally adjusted for other metabolic syndrome risk factors. In men and women Kaplan-Meier survival curves according to HDL and TG levels revealed that participants with metabolic dyslipidemia had poorer survival compared to people without metabolic dyslipidemia (logrank p<0.001 for each). CONCLUSIONS: Metabolic dyslipidemia is associated with an increased risk of CHD. This relationship was independent from LDL-C and other risk factors of the metabolic syndrome in men, but not in women. A better management of this phenotype via lifestyle modification or pharmacotherapy may be warranted.

LDL-C-lowering therapy: current and future therapeutic targets.

Recent trials have emphasized that more intensive low-density lipoprotein cholesterol (LDL-C) lowering results in a further reduction in cardiovascular disease risk. Uptitration of statins has limited incremental LDL-C-lowering effects and leads to an increased incidence of side effects. Therefore, attention has shifted toward alternative LDL-C-lowering modalities. Several promising compounds have entered the clinical trial arena, although with mixed results. Acyl-coenzyme A: cholesterol O-acyltransferase (ACAT) inhibitors failed to show benefit. Microsomal triglyceride transfer protein and squalene synthase inhibitors, in spite of beneficial lipid profile changes, have shown adverse event profiles. In contrast, inhibitors of intestinal cholesterol absorption have shown LDL-C-lowering efficacy associated with few side effects. The inhibition of apolipoprotein B100 synthesis by antisense oligonucleotides has now been tested in phase 2 clinical trials, with promising results. Finally, compounds modifying protein convertase subtilisin/kexin type 9 levels are currently in the preclinical phase. In the present article, we discuss these LDL-C-lowering strategies.