Comparative Effects of PCSK9 (Proprotein Convertase Subtilisin/Kexin Type 9) Inhibition and Statins on Postprandial Triglyceride-Rich Lipoprotein Metabolism

Acute Statin Withdrawal Does not Interfere With the Improvements of a Session of Exercise in Postprandial Metabolism

BACKGROUND

The risk for atherogenic plaque formation is high after ingestion of meals in individuals with high blood lipid levels (ie, dyslipidemia). Statins and exercise reduce the rise of blood triglyceride concentrations after a meal, but the effect of their combination is unclear.

METHODS

In a randomized crossover design, 11 individuals with dyslipidemia and metabolic syndrome treated with statins underwent a mixed-meal (970 ± 111 kcal, 24% fat, and 34% carbohydrate) tolerance test. Plasma lipid concentrations, fat oxidation, glucose, and glycerol kinetics were monitored immediately prior and during the meal test. Trials were conducted with participants under their habitual statin treatment and 96 hours after blinded statin withdrawal. Trials were duplicated after a prolonged bout of low-intensity exercise (75 minutes at 53 ± 4% maximal oxygen consumption) to study the interactions between exercise and statins.

RESULTS

Statins reduced postprandial plasma triglycerides from 3.03 ± 0.85 to 2.52 ± 0.86 mmol·L-1 (17%; P = .015) and plasma glycerol concentrations (ie, surrogate of whole-body lipolysis) without reducing plasma free fatty acid concentration or fat oxidation. Prior exercise increased postprandial plasma glycerol levels (P = .029) and fat oxidation rates (P = .024). Exercise decreased postprandial plasma insulin levels (241 ± 116 vs 301 ± 172 ρmol·L-1; P = .026) but not enough to increase insulin sensitivity (P = .614). Neither statins nor exercise affected plasma glucose appearance rates from exogenous or endogenous sources.

CONCLUSIONS

In dyslipidemic individuals, statins reduce blood triglyceride concentrations after a meal, but without limiting fat oxidation. Statins do not interfere with exercise lowering the postprandial insulin that likely promotes fat oxidation. Last, statins do not restrict the rates of plasma incorporation or oxidation of the ingested glucose.

Contribution of intestinal triglyceride-rich lipoproteins to residual atherosclerotic cardiovascular disease risk in individuals with type 2 diabetes on statin therapy

AIMS/HYPOTHESIS

This study explored the hypothesis that significant abnormalities in the metabolism of intestinally derived lipoproteins are present in individuals with type 2 diabetes on statin therapy. These abnormalities may contribute to residual CVD risk.

METHODS

To investigate the kinetics of ApoB-48- and ApoB-100-containing lipoproteins, we performed a secondary analysis of 11 overweight/obese individuals with type 2 diabetes who were treated with lifestyle counselling and on a stable dose of metformin who were from an earlier clinical study, and compared these with 11 control participants frequency-matched for age, BMI and sex. Participants in both groups were on a similar statin regimen during the study. Stable isotope tracers were used to determine the kinetics of the following in response to a standard fat-rich meal: (1) apolipoprotein (Apo)B-48 in chylomicrons and VLDL; (2) ApoB-100 in VLDL, intermediate-density lipoprotein (IDL) and LDL; and (3) triglyceride (TG) in VLDL.

RESULTS

The fasting lipid profile did not differ significantly between the two groups. Compared with control participants, in individuals with type 2 diabetes, chylomicron TG and ApoB-48 levels exhibited an approximately twofold higher response to the fat-rich meal, and a twofold higher increment was observed in ApoB-48 particles in the VLDL1 and VLDL2 density ranges (all p < 0.05). Again comparing control participants with individuals with type 2 diabetes, in the latter, total ApoB-48 production was 25% higher (556 ± 57 vs 446 ± 57 mg/day; p < 0.001), conversion (fractional transfer rate) of chylomicrons to VLDL was around 40% lower (35 ± 25 vs 82 ± 58 pools/day; p=0.034) and direct clearance of chylomicrons was 5.6-fold higher (5.6 ± 2.2 vs 1.0 ± 1.8 pools/day; p < 0.001). During the postprandial period, ApoB-48 particles accounted for a higher proportion of total VLDL in individuals with type 2 diabetes (44%) compared with control participants (25%), and these ApoB-48 VLDL particles exhibited a fivefold longer residence time in the circulation (p < 0.01). No between-group differences were seen in the kinetics of ApoB-100 and TG in VLDL, or in LDL ApoB-100 production, pool size and clearance rate. As compared with control participants, the IDL ApoB-100 pool in individuals with type 2 diabetes was higher due to increased conversion from VLDL2.

CONCLUSIONS/INTERPRETATION

Abnormalities in the metabolism of intestinally derived ApoB-48-containing lipoproteins in individuals with type 2 diabetes on statins may help to explain the residual risk of CVD and may be suitable targets for interventions.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02948777.

Novel and future lipid-modulating therapies for the prevention of cardiovascular disease

Lowering the levels of LDL cholesterol in the plasma has been shown to reduce the risk of atherosclerotic cardiovascular disease (ASCVD). Several other lipoproteins, such as triglyceride-rich lipoproteins, HDL and lipoprotein(a) are associated with atherosclerosis and ASCVD, with strong evidence supporting causality for some. In this Review, we discuss novel and upcoming therapeutic strategies targeting different pathways in lipid metabolism to potentially attenuate the risk of cardiovascular events. Key proteins involved in lipoprotein metabolism, such as PCSK9, angiopoietin-related protein 3, cholesteryl ester transfer protein and apolipoprotein(a), have been identified as viable targets for therapeutic intervention through observational and genetic studies. These proteins can be targeted using a variety of approaches, such as protein inhibition or interference, inhibition of translation at the mRNA level (with the use of antisense oligonucleotides or small interfering RNA), and the introduction of loss-of-function mutations through base editing. These novel and upcoming strategies are complementary to and could work synergistically with existing therapies, or in some cases could potentially replace therapies, offering unprecedented opportunities to prevent ASCVD. Moreover, a major challenge in the prevention and treatment of non-communicable diseases is how to achieve safe, long-lasting reductions in causal exposures. This challenge might be overcome with approaches such as small interfering RNAs or genome editing, which shows how far the field has advanced from when the burden of achieving this goal was placed upon patients through rigorous adherence to daily small-molecule drug regimens.

Composition and distribution of lipoproteins after evolocumab in familial dysbetalipoproteinemia: A randomized controlled trial

BACKGROUND

Proprotein convertase subtilisin kexin type 9 (PCSK9) monoclonal antibodies (mAbs) reduce fasting and post fat load cholesterol in non-HDL and intermediate density lipoprotein (IDL) in familial dysbetalipoproteinemia (FD). However, the effect of PCSK9 mAbs on the distribution and composition of atherogenic lipoproteins in patients with FD is unknown.

OBJECTIVE

To evaluate the effect of the PCSK9 mAb evolocumab added to standard lipid-lowering therapy in patients with FD on fasting and post fat load lipoprotein distribution and composition.

METHODS

Randomized placebo-controlled double-blind crossover trial comparing evolocumab (140 mg subcutaneous every 2 weeks) with placebo during two 12-week treatment periods. Patients received an oral fat load at the start and end of each treatment period. Apolipoproteins (apo) were measured with ultracentrifugation, gradient gel electrophoresis, retinyl palmitate and SDS-PAGE.

RESULTS

PCSK9 mAbs significantly reduced particle number of all atherogenic lipoproteins, with a stronger effect on smaller lipoproteins than on larger lipoproteins (e.g. IDL-apoB 49%, 95%confidence interval (CI) 41-59 and very low-density lipoprotein (VLDL)-apoB 33%, 95%CI 16-50). Furthermore, PCSK9 mAbs lowered cholesterol more than triglyceride (TG) in VLDL, IDL and low-density lipoprotein (LDL) (e.g. VLDL-C 48%, 95%CI 29-63%; and VLDL-TG 20%, 95%CI 6.3-41%). PCSK9 mAbs did not affect the post fat load response of chylomicrons.

CONCLUSION

PCSK9 mAbs added to standard lipid-lowering therapy in FD patients significantly reduced lipoprotein particle number, in particular the smaller and more cholesterol-rich lipoproteins (i.e. IDL and LDL). PCSK9 mAbs did not affect chylomicron metabolism. It seems likely that the observed effects are achieved by increased hepatic lipoprotein clearance, but the specific working mechanism of PCSK9 mAbs in FD patients remains to be elucidated.

Structure-activity relationship and biological evaluation of xanthine derivatives as PCSK9 inhibitors for the treatment of atherosclerosis

Developing non-statin small molecules for the treatment of hypercholesterolemia remains challenging. The proprotein convertase subtilisin/kexin type 9 (PCSK9)-targeted therapies have attracted considerable attentions. Forty-five 7030B-C5 derivatives were synthesized and evaluated for the PCSK9 repression activity, taking the PCSK9 transcriptional inhibitor 7030B-C5 as the lead. Structure-activity relationship (SAR) analysis at C8 and N7-position was carried out, and compound 3s and 5r exhibited comparable PCSK9 transcriptional inhibitory activity but much lower cytotoxicity with the therapeutic index (TI) values doubled of that of 7030B-C5. In the in vitro assay, both compounds significantly reduced the level of PCSK9 protein and increased LDL receptor (LDLR) protein level. What's more, both compounds promoted LDL cholesterol (LDL-C) clearance more efficiently than 7030B-C5 in HepG2 cells. Most importantly, compound 3s reduced the atherosclerotic plaque areas with promising lipid-lowing effects in ApoE KO mice with a higher in vivo activity and lower toxicity. The regulatory mechanism of 3s was explored that it might target the transcription factor HNF1α and/or HINFP upstream of PCSK9 transcription, similar to that of 7030B-C5. Thus, 3s was considered as a potential anti-atherosclerosis drug candidate as a novel PCSK9 down-regulatory agent, worthy of further investigations.

Effectiveness of statins vs. exercise on reducing postprandial hypertriglyceridemia in dyslipidemic population: A systematic review and network meta-analysis

BACKGROUND

Individuals at risk of suffering cardiovascular disease (CVD) present with larger increases in blood triglyceride (TG) concentration after a high-fat meal than do healthy individuals. These postprandial hypertriglyceride levels are an independent risk factor for CVD. Prescription of statins and a bout of prolonged exercise are both effective in lowering postprandial hypertriglyceride levels. We aimed to evaluate the comparative effectiveness of statins vs. a bout of aerobic exercise in reducing fasting and postprandial TG (PPTG) concentrations in individuals at high risk of developing CVD.

METHODS

Thirty-seven studies from a systematic literature search of the PubMed, EMBASE, and Cochrane databases were included in this review. The selected studies conducted trials involving statin therapy (n = 20) or a bout of aerobic exercise (n = 19) and measured their impact on PPTG levels as the outcome. Two studies analyzed both treatments and were included in duplicate. The meta-analysis was constructed using a random-effects model to calculate the mean difference (MD). The Student t test was used to compare the data sets for statins vs. exercise.

RESULTS

Overall, statin and exercise interventions showed similar reductions in PPTG levels, with an MD of -0.65 mmol/L for statins (95% confidence interval (95%CI): -0.54 to -0.77; p < 0.001) and -0.46 mmol/L for exercise (95%CI: -0.21 to -0.71; p < 0.01). However, statins lowered fasting TG levels more than exercise (MD = -1.54 mmol/L, 95%CI: -2.25 to -0.83; p = 0.009).

CONCLUSION

Although aerobic exercise is effective in lowering blood TG levels, statins seem to be more efficient, especially in the fasted state. A combination of exercise and statins might reveal a valuable approach to the treatment and prevention of CVD. More studies are required to determine the underlying mechanisms and the possible additive effects of these interventions.

Metabolism of triglyceride-rich lipoproteins in health and dyslipidaemia

Accumulating evidence points to the causal role of triglyceride-rich lipoproteins and their cholesterol-enriched remnants in atherogenesis. Genetic studies in particular have not only revealed a relationship between plasma triglyceride levels and the risk of atherosclerotic cardiovascular disease, but have also identified key proteins responsible for the regulation of triglyceride transport. Kinetic studies in humans using stable isotope tracers have been especially useful in delineating the function of these proteins and revealing the hitherto unappreciated complexity of triglyceride-rich lipoprotein metabolism. Given that triglyceride is an essential energy source for mammals, triglyceride transport is regulated by numerous mechanisms that balance availability with the energy demands of the body. Ongoing investigations are focused on determining the consequences of dysregulation as a result of either dietary imprudence or genetic variation that increases the risk of atherosclerosis and pancreatitis. The identification of molecular control mechanisms involved in triglyceride metabolism has laid the groundwork for a 'precision-medicine' approach to therapy. Novel pharmacological agents under development have specific molecular targets within a regulatory framework, and their deployment heralds a new era in lipid-lowering-mediated prevention of disease. In this Review, we outline what is known about the dysregulation of triglyceride transport in human hypertriglyceridaemia.

Emerging Insights on the Diverse Roles of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) in Chronic Liver Diseases: Cholesterol Metabolism and Beyond

Chronic liver diseases are commonly associated with dysregulated cholesterol metabolism. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease of the proprotein convertase family that is mainly synthetized and secreted by the liver, and represents one of the key regulators of circulating low-density lipoprotein (LDL) cholesterol levels. Its ability to bind and induce LDL-receptor degradation, in particular in the liver, increases circulating LDL-cholesterol levels in the blood. Hence, inhibition of PCSK9 has become a very potent tool for the treatment of hypercholesterolemia. Besides PCSK9 limiting entry of LDL-derived cholesterol, affecting multiple cholesterol-related functions in cells, more recent studies have associated PCSK9 with various other cellular processes, including inflammation, fatty acid metabolism, cancerogenesis and visceral adiposity. It is increasingly becoming evident that additional roles for PCSK9 beyond cholesterol homeostasis are crucial for liver physiology in health and disease, often contributing to pathophysiology. This review will summarize studies analyzing circulating and hepatic PCSK9 levels in patients with chronic liver diseases. The factors affecting PCSK9 levels in the circulation and in hepatocytes, clinically relevant studies and the pathophysiological role of PCSK9 in chronic liver injury are discussed.

Recent dynamic studies of the metabolism of atherogenic lipoproteins: elucidating the mode of action of new therapies

PURPOSE OF REVIEW

LDL, triglyceride-rich lipoprotein (TRL) and lipoprotein(a) [Lp(a)] particles are the key atherogenic lipoproteins. Deranged metabolism of these lipoproteins accounts for a spectrum of clinically important dyslipidemias, such as FH, elevated Lp(a) and diabetic dyslipidemia. We review the findings from recent dynamic and tracer studies that have contributed to expanding knowledge in this field.

RECENT FINDINGS

Deficiency in LDL receptor activity does not only impair the catabolism of LDL-apoB-100 in FH, but also induces hepatic overproduction and decreases catabolism of TRLs. Patients with elevated Lp(a) are characterized by increased hepatic secretion of Lp(a) particles. Elevation of TRLs in diabetes is partly mediated by increased production of apoB-48 and apoC-III, and impaired clearance of apoB-48 in the postprandial state. Tracer kinetic studies show that proprotein convertase subtilisin/kexin type 9 mAbs alone or in combination with statin can increase the catabolism and decrease production of LDL and Lp(a) particles. By contrast, angiopoietin-like protein 3 inhibitors (e.g. evinacumab) reduce VLDL production and increase LDL clearance in FH. Glucagon-like peptide-1 receptor agonists can improve diabetic dyslipidemia by increasing the catabolism of apoB-48 and decreasing the production of apoB-48 and apoC-III.

SUMMARY

Dynamic studies of the metabolism of atherogenic lipoproteins provide new insight into the nature of dyslipidemias and point to how new therapies with complementary modes of action may have maximal clinical impact.

PCSK9 E670G (rs505151) Variant and Coronary Artery Disease Risk Among Diabetics

Background: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an enzyme in the family of proprotein convertases implicated in lipid metabolism and is a significant genetic risk factor in cardiovascular diseases among various populations. Aim of the Study: This study explored the correlation between the alleles of the rs505151 (E670G) locus of the PCSK9 gene and its expression levels with coronary artery disease (CAD) risk in Egyptian patients with type 2 diabetes mellitus (T2DM). Subjects and Methods: A case-control study was performed on 112 lean subjects compared to 100 T2DM patients without CAD and 84 T2DM patients with CAD to investigate the relationships among PCSK9 expression levels, the E670G (rs505151) gene variant, lipid concentrations, and CAD risk in an Egyptian diabetic population. A restriction fragment length polymorphism-polymerase chain reaction (PCR) assay was used to assess the gene polymorphism, and PCSK9 mRNA expression was determined by quantitative real-time PCR. Results: The prevalence of the E670G (rs505151) AG genotype in diabetics with CAD was significantly greater than the other two groups. The PCSK9 gene expression levels in diabetics with CAD were significantly greater than the other two groups. G allele carriers (AG+GG) had a higher relative PCSK9 expression than A allele carriers. Conclusion: PCSK9 relative expression levels and the E670G (rs505151) AG genotype are CAD risk factors among Egyptian diabetics and are linked positively to the atherogenic index of plasma.

Effects of liraglutide on the metabolism of triglyceride-rich lipoproteins in type 2 diabetes

AIM

To elucidate the impact of liraglutide on the kinetics of apolipoprotein (apo)B48- and apoB100-containing triglyceride-rich lipoproteins in subjects with type 2 diabetes (T2D) after a single fat-rich meal.

MATERIALS AND METHODS

Subjects with T2D were included in a study to investigate postprandial apoB48 and apoB100 metabolism before and after 16 weeks on l.8 mg/day liraglutide (n = 14) or placebo (n = 4). Stable isotope tracer and compartmental modelling techniques were used to determine the impact of liraglutide on chylomicron and very low-density lipoprotein (VLDL) production and clearance after a single fat-rich meal.

RESULTS

Liraglutide reduced apoB48 synthesis in chylomicrons by 60% (p < .0001) and increased the triglyceride/apoB48 ratio (i.e. the size) of chylomicrons (p < .001). Direct clearance of chylomicrons, a quantitatively significant pathway pretreatment, decreased by 90% on liraglutide (p < .001). Liraglutide also reduced VLDL₁ -triglyceride secretion (p = .017) in parallel with reduced liver fat. Chylomicron-apoB48 production and particle size were related to insulin sensitivity (p = .015 and p < .001, respectively), but these associations were perturbed by liraglutide.

CONCLUSIONS

In a physiologically relevant setting that mirrored regular feeding in subjects with T2D, liraglutide promoted potentially beneficial changes on postprandial apoB48 metabolism. Using our data in an integrated metabolic model, we describe how the action of liraglutide in T2D on chylomicron and VLDL kinetics could lead to decreased generation of remnant lipoproteins.

Mechanisms of Atherosclerosis Induced by Postprandial Lipemia

Postprandial lipemia plays an important role in the formation, occurrence, and development of atherosclerosis, and it is closely related to coronary heart disease and other diseases involving endothelial dysfunction, oxidative stress, inflammation, and other mechanisms. Therefore, it has become a focus area for further research. The studies on postprandial lipemia mainly include TG, TRL, VLDL, CM, and remnant cholesterol. Diurnal triglyceride patterns and postprandial hyperlipidemia are very relevant and are now insufficiently covered. The possible mechanisms between postprandial lipemia and cardiovascular disease have been reviewed in this article by referring to relevant literature in recent years. The research progress on the effects of postprandial lipemia on endothelial function, oxidative stress, and inflammation is highlighted. The intervention of postprandial lipemia is discussed. Non-medicinal intervention such as diet and exercise improves postprandial lipemia. As medicinal intervention, statin, fibrate, ezetimibe, omega-3 fatty acids, and niacin have been found to improve postprandial lipid levels. Novel medications such as pemafibrate, PCSK9, and apoCIII inhibitors have been the focus of research in recent years. Gut microbiota is closely related to lipid metabolism, and some studies have indicated that intestinal microorganisms may affect lipid metabolism as environmental factors. Whether intervention of gut microbiota can reduce postprandial lipemia, and therefore against AS, may be worthy of further study.

New Insights Into the Regulation of Lipoprotein Metabolism by PCSK9: Lessons From Stable Isotope Tracer Studies in Human Subjects

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a convertase enzyme mostly produced by the liver. It is a key regulator of LDL metabolism because of its ability to enhance degradation of the LDL receptor. PCSK9 also regulates the metabolism of lipoprotein(a) [Lp(a)] and triglyceride-rich lipoproteins (TRLs). Its key role in modulating atherosclerotic cardiovascular disease (ASCVD) is supported by genetic studies and clinical outcome trials. Kinetic studies provide mechanistic insight into the role of PCSK9 in regulating the physiology and pathophysiology of plasma lipids and lipoproteins. Kinetic data have demonstrated that plasma PCSK9 concentration is inversely associated with the clearance of LDL in men. Gain-of-function mutations of PCSK9 markedly increase plasma LDL-cholesterol concentrations due to impaired LDL-apoB catabolism. Conversely, PCSK9 deficiency results in low LDL-cholesterol associated with enhanced LDL-apoB clearance. Inhibition of PCSK9 with monoclonal antibodies (such as evolocumab or alirocumab) lowers plasma LDL-cholesterol and apoB levels chiefly by upregulating the catabolism of LDL particles in healthy individuals. As monotherapy, PCSK9 inhibitor reduced Lp(a) concentrations by decreasing the production rate. However, as combination therapy, it reduced the plasma concentration of Lp(a) by increasing the fractional catabolism of Lp(a) particles. In statin-treated patients with high Lp(a), PCSK9 inhibition lowers plasma Lp(a) concentrations by accelerating the catabolism of Lp(a) particles. The effect of PCSK9 inhibition on TRL metabolism has been studied in healthy individuals and in patients with type 2 diabetes. These findings suggest that PCSK9 appears to play a less important role in TRL than LDL metabolism. Kinetic studies of PCSK9 inhibition therapy on lipoprotein metabolism in diverse high risk patient populations (such as familial hypercholesterolemia) and new therapeutic combination also merit further investigation.

Effects of Evolocumab on the Postprandial Kinetics of Apo (Apolipoprotein) B100- and B48-Containing Lipoproteins in Subjects With Type 2 Diabetes

OBJECTIVE

Increased risk of atherosclerotic cardiovascular disease in subjects with type 2 diabetes is linked to elevated levels of triglyceride-rich lipoproteins and their remnants. The metabolic effects of PCSK9 (proprotein convertase subtilisin/kexin 9) inhibitors on this dyslipidemia were investigated using stable-isotope-labeled tracers. Approach and Results: Triglyceride transport and the metabolism of apos (apolipoproteins) B48, B100, C-III, and E after a fat-rich meal were investigated before and on evolocumab treatment in 13 subjects with type 2 diabetes. Kinetic parameters were determined for the following: apoB48 in chylomicrons; triglyceride in VLDL₁ (very low-density lipoprotein) and VLDL₂; and apoB100 in VLDL₁, VLDL₂, IDL (intermediate-density lipoprotein), and LDL (low-density lipoprotein). Evolocumab did not alter the kinetics of apoB48 in chylomicrons or apoB100 or triglyceride in VLDL₁. In contrast, the fractional catabolic rates of VLDL₂-apoB100 and VLDL₂-triglyceride were both increased by about 45%, which led to a 28% fall in the VLDL₂ plasma level. LDL-apoB100 was markedly reduced by evolocumab, which was linked to metabolic heterogeneity in this fraction. Evolocumab increased clearance of the more rapidly metabolized LDL by 61% and decreased production of the more slowly cleared LDL by 75%. ApoC-III kinetics were not altered by evolocumab, but the apoE fractional catabolic rates increased by 45% and the apoE plasma level fell by 33%. The apoE fractional catabolic rates was associated with the decrease in VLDL₂- and IDL-apoB100 concentrations.

CONCLUSIONS

Evolocumab had only minor effects on lipoproteins that are involved in triglyceride transport (chylomicrons and VLDL₁) but, in contrast, had a profound impact on lipoproteins that carry cholesterol (VLDL₂, IDL, LDL). Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02948777.

Apolipoprotein B48 metabolism in chylomicrons and very low-density lipoproteins and its role in triglyceride transport in normo- and hypertriglyceridemic human subjects

BACKGROUND

Renewed interest in triglyceride-rich lipoproteins as causative agents in cardiovascular disease mandates further exploration of the integrated metabolism of chylomicrons and very low-density lipoproteins (VLDL).

METHODS

Novel tracer techniques and an integrated multi-compartmental model were used to determine the kinetics of apoB48- and apoB100-containing particles in the chylomicron and VLDL density intervals in 15 subjects with a wide range of plasma triglyceride levels.

RESULTS

Following a fat-rich meal, apoB48 appeared in the chylomicron, VLDL₁ and VLDL₂ fractions in all subjects. Chylomicrons cleared rapidly from the circulation but apoB48-containing VLDL accumulated, and over the day were 3-fold higher in those with high versus low plasma triglyceride. ApoB48-containing particles were secreted directly into both the chylomicron and VLDL fractions at rates that were similar across the plasma triglyceride range studied. During fat absorption, whilst most triglyceride entered the circulation in chylomicrons, the majority of apoB48 particles were secreted into the VLDL density range.

CONCLUSION

The intestine secretes apoB48-containing particles not only as chylomicrons but also directly into the VLDL₁ and VLDL₂ density ranges both in the basal state and during dietary lipid absorption. Over the day, apoB48-containing particles appear to comprise about 20-25% of circulating VLDL and, especially in those with elevated triglycerides, form part of a slowly cleared 'remnant' particle population, thereby potentially increasing CHD risk. These findings provide a metabolic understanding of the potential consequences for increased CHD risk when slowed lipolysis leads to the accumulation of remnants, especially in individuals with hypertriglyceridemia.

Circulating Rather Than Intestinal PCSK9 (Proprotein Convertase Subtilisin Kexin Type 9) Regulates Postprandial Lipemia in Mice

OBJECTIVE

Increased postprandial lipemia (PPL) is an independent risk factor for atherosclerotic cardiovascular diseases. PCSK9 (Proprotein convertase subtilisin kexin type 9) is an endogenous inhibitor of the LDLR (low-density lipoprotein receptor) pathway. We previously showed that PCSK9 inhibition in mice reduces PPL. However, the relative contribution of intracellular intestinal PCSK9 or liver-derived circulating PCSK9 to this effect is still unclear. Approach and Results: To address this issue, we generated the first intestine-specific Pcsk9-deficient (i-Pcsk9^-/-) mouse model. PPL was measured in i-Pcsk9^-/- as well as in wild-type and streptozotocin-induced diabetic mice following treatment with a PCSK9 monoclonal antibody (alirocumab). Blocking the circulating form of PCSK9 with alirocumab significantly reduced PPL, while overexpressing human PCSK9 in the liver of full Pcsk9^-/- mice had the opposite effect. Alirocumab regulated PPL in a LDLR-dependent manner as this effect was abolished in Ldlr^-/- mice. In contrast, i-Pcsk9^-/- mice did not exhibit alterations in plasma lipid parameters nor in PPL. Finally, PPL was highly exacerbated by streptozotocin-induced diabetes mellitus in Pcsk9^+/+ but not in Pcsk9^-/- mice, an effect that was mimicked by the use of alirocumab in streptozotocin-treated Pcsk9^+/+ mice.

CONCLUSIONS

Taken together, our data demonstrate that PPL is significantly altered by full but not intestinal PCSK9 deficiency. Treatment with a PCSK9 monoclonal antibody mimics the effect of PCSK9 deficiency on PPL suggesting that circulating PCSK9 rather than intestinal PCSK9 is a critical regulator of PPL. These data validate the clinical relevance of PCSK9 inhibitors to reduce PPL, especially in patients with type 2 diabetes mellitus.

Effects of statins and exercise on postprandial lipoproteins in metabolic syndrome vs metabolically healthy individuals

AIMS

To determine if the combination of exercise and statin could normalize postprandial triglyceridaemia (PPTG) in hypercholesteraemic individuals.

METHODS

Eight hypercholesteraemic (blood cholesterol 182 ± 38 mg dL^-1 ; low-density lipoprotein-cholesterol [LDL-c] 102 ± 32 mg dL^-1 ) overweight (body mass index 30 ± 4 kg m^-2 ) individuals with metabolic syndrome (MetS) were compared to a group of 8 metabolically healthy (MetH) controls (blood cholesterol 149 ± 23 mg dL^-1 ; LDL-c 77 ± 23 mg dL^-1 , and body mass index 23 ± 2 kg m^-2 ). Each group underwent 2 PPTG tests, either 14 hours after a bout of intense exercise or without previous exercise. Additionally, MetS individuals were tested 96 hours after withdrawal of their habitual statin medication to study medication effects.

RESULTS

A bout of exercise before the test meal did not reduce PPTG in MetS (P = .347), but reduced PPTG by 46% in MetH (413 ± 267 to 224 ± 142 mg dL^-1 for 5 h incremental area under the curve; P = .02). In both trials (i.e., either after a bout of intense exercise or without previous exercise), statin withdrawal in MetS greatly increased PPTG (average 65%; P < .01), mean LDL-c (average 25%; P < .01), total cholesterol (average 16%; P < .01) and apolipoprotein (Apo) B48 (24%; P < .01), without interference from exercise. However, Apo B100 was not affected by statin withdrawal.

CONCLUSION

Hypercholesteraemic MetS individuals (compared to MetH controls) fail to show an effect of exercise on reducing PPTG. However, chronic statin medication blunts the elevations in triglyceride after a fat meal (i.e., incremental area under the curve of PPTG) reducing their cardiovascular risk associated with their atherogenic dyslipidaemia. Statin decreases PPTG by reducing the secretion or accelerating the catabolism of intestinal Apo B48.

A placebo-controlled proof-of-concept study of alirocumab on postprandial lipids and vascular elasticity in insulin-treated patients with type 2 diabetes mellitus

AIM

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of cardiovascular disease (CVD) linked to atherogenic dyslipidaemia and postprandial hyperlipidaemia. Alirocumab, a proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor, improves CVD risk by reducing the concentration of low-density lipoprotein-cholesterol (LDL-C). However, effects of PCK9 inhibitors on other aspects of diabetic dyslipidaemia, particularly in the postprandial situation, are less clear.

MATERIAL AND METHODS

Twelve male patients with T2DM on an intensive insulin regimen completed a 6-week randomized, double-blind, placebo-controlled, proof-of-concept study. Participants received three biweekly dosages of subcutaneous alirocumab (150 mg) or placebo. Before and after the intervention, fasting and postprandial triglyceride (TG) plasma levels, apolipoprotein (apo) B48, lipoprotein composition isolated by ultracentrifugation, vascular function and markers of inflammation were evaluated.

RESULTS

Alirocumab treatment reduced fasting plasma TG levels (between group median change -24.7%; P = 0.018) and fasting apoB48 serum levels (-35.9%; P = 0.039) compared with placebo. Alirocumab reduced the plasma TG area under the curve (AUC) (-26.4%; P = 0.006) and apoB48 AUC (-55.7%; P = 0.046), as well as plasma TG incremental AUC (-21.4%; P = 0.04) and apoB48 incremental AUC (-26.8%; P = 0.02). In addition, alirocumab reduced fasting and postprandial TG levels in very low-density lipoprotein (VLDL) and LDL. Alirocumab improved fasting pulse wave velocity, but no changes in postprandial markers of inflammation were observed.

CONCLUSIONS

In addition to the well-known LDL-C-reducing effects, 6 weeks of alirocumab treatment lowered both fasting and postprandial plasma TG levels by reducing the TG levels in VLDL and LDL and the concentration of intestinal remnants.

Research progress on alternative non-classical mechanisms of PCSK9 in atherosclerosis in patients with and without diabetes

The proprotein convertase subtilisin/kexin type 9 (PCSK9) acts via a canonical pathway to regulate circulating low-density lipoprotein-cholesterol (LDL-C) via degradation of the LDL receptor (LDLR) on the liver cell surface. Published research has shown that PCSK9 is involved in atherosclerosis via a variety of non-classical mechanisms that involve lysosomal, inflammatory, apoptotic, mitochondrial, and immune pathways. In this review paper, we summarized these additional mechanisms and described how anti-PCSK9 therapy exerts effects through these mechanisms. These additional pathways further illustrate the regulatory role of PCSK9 in atherosclerosis and offer an in-depth interpretation of how the PCSK9 inhibitor exerts effects on the treatment of atherosclerosis.

Causes and Consequences of Hypertriglyceridemia

Elevations in plasma triglyceride are the result of overproduction and impaired clearance of triglyceride-rich lipoproteins-very low-density lipoproteins (VLDL) and chylomicrons. Hypertriglyceridemia is characterized by an accumulation in the circulation of large VLDL-VLDL₁-and its lipolytic products, and throughout the VLDL-LDL delipidation cascade perturbations occur that give rise to increased concentrations of remnant lipoproteins and small, dense low-density lipoprotein (LDL). The elevated risk of atherosclerotic cardiovascular disease in hypertriglyceridemia is believed to result from the exposure of the artery wall to these aberrant lipoprotein species. Key regulators of the metabolism of triglyceride-rich lipoproteins have been identified and a number of these are targets for pharmacological intervention. However, a clear picture is yet to emerge as to how to relate triglyceride lowering to reduced risk of atherosclerosis.

Role of the Gut in Diabetic Dyslipidemia

Type 2 diabetes (T2D) is associated with increased risk of cardiovascular disease (CVD). In insulin resistant states such as the metabolic syndrome, overproduction and impaired clearance of liver-derived very-low-density lipoproteins and gut-derived chylomicrons (CMs) contribute to hypertriglyceridemia and elevated atherogenic remnant lipoproteins. Although ingested fat is the major stimulus of CM secretion, intestinal lipid handling and ultimately CM secretory rate is determined by numerous additional regulatory inputs including nutrients, hormones and neural signals that fine tune CM secretion during fasted and fed states. Insulin resistance and T2D represent perturbed metabolic states in which intestinal sensitivity to key regulatory hormones such as insulin, leptin and glucagon-like peptide-1 (GLP-1) may be altered, contributing to increased CM secretion. In this review, we describe the evidence from human and animal models demonstrating increased CM secretion in insulin resistance and T2D and discuss the molecular mechanisms underlying these effects. Several novel compounds are in various stages of preclinical and clinical investigation to modulate intestinal CM synthesis and secretion. Their efficacy, safety and therapeutic utility are discussed. Similarly, the effects of currently approved lipid modulating therapies such as statins, ezetimibe, fibrates, and PCSK9 inhibitors on intestinal CM production are discussed. The intricacies of intestinal CM production are an active area of research that may yield novel therapies to prevent atherosclerotic CVD in insulin resistance and T2D.

Impact of proprotein convertase subtilisin/kexin type 9 inhibition with evolocumab on the postprandial responses of triglyceride-rich lipoproteins in type II diabetic subjects

BACKGROUND

Monoclonal antibodies to proprotein convertase subtilisin/kexin type 9 (PCSK9) significantly lower the levels of low-density lipoprotein and very-low-density lipoproteins (VLDL), but their effect on postprandial lipoprotein metabolism in dyslipidemic subjects is unclear.

OBJECTIVE

This study aimed to investigate the effects of evolocumab on postprandial lipid responses, ectopic fat depots, whole-body cholesterol synthesis, hepatic lipogenesis, and fat oxidation in patients with type II diabetes.

METHODS

The trial was a single-phase, nonrandomized study of 12-week treatment with evolocumab 140 mg subcutaneously every 2 weeks in 15 patients with type II diabetes on background statin therapy. Cardiometabolic responses to a high-fat mixed meal were assessed before and at the end of the intervention period.

RESULTS

Evolocumab treatment reduced significantly postprandial rises in plasma total triglyceride (by 21%; P < .0001) and VLDL₁ triglyceride (by 15%; P = .018), but the increase in chylomicron triglyceride after the meal was not significantly perturbed (P = .053). There were reduced postprandial responses in plasma total apolipoprotein C-III (by 14%; P < .0001) and apolipoprotein B-48 concentration (by 17%; P = .0046) and in "remnant-like particles" cholesterol (by 29%; P < .0001) on the PCSK9 inhibitor. Treatment reduced the steady-state (ie, fasting and postprandial) concentrations of VLDL₂ cholesterol by 50% (P < .0001) and VLDL₂ triglyceride by 29% (P < .0001), in addition to the 78% reduction of low-density lipoprotein cholesterol (P < .001). The changes in apolipoprotein C-III associated significantly with reduction in postprandial responses of remnant-like particles cholesterol and triglyceride-rich lipoprotein cholesterol. Evolocumab therapy did not influence liver fat accumulation, hepatic de novo lipogenesis, or fasting β-hydroxybutyrate but did increase total body cholesterol synthesis (P < .01).

CONCLUSION

Evolocumab treatment improved postprandial responses of triglyceride-rich lipoproteins and measures of cholesterol-enriched remnant particles in type II diabetic subjects. These results indicate that postprandial phenomena need to be taken into account in assessing the full range of actions of PCSK9 inhibitors in dyslipidemic individuals.

Efficacy and safety of evolocumab in individuals with type 2 diabetes mellitus: primary results of the randomised controlled BANTING study

AIMS/HYPOTHESIS

The study aimed to examine the efficacy of 12 weeks of monthly evolocumab or placebo in lowering LDL-cholesterol (LDL-C) in individuals with type 2 diabetes and hypercholesterolaemia or mixed dyslipidaemia and on a maximum-tolerated statin of at least moderate intensity.

METHODS

For this randomised, placebo-controlled outpatient study, eligible individuals were ≥18 years old with type 2 diabetes, HbA_1c <10% (86 mmol/mol), had been on stable pharmacological therapy for diabetes for ≥6 months and were taking a maximum-tolerated statin dose of at least moderate intensity. Lipid eligibility criteria varied by history of clinical cardiovascular disease. Participants were randomised 2:1 to evolocumab 420 mg s.c. or placebo. Randomisation was performed centrally via an interactive web-based or voice recognition system. Allocation was concealed using the centralised randomisation process. Treatment assignment was blinded to the sponsor study team, investigators, site staff and patients throughout the study. Co-primary endpoints were mean percentage change in LDL-C from baseline to week 12 and to the mean of weeks 10 and 12. Additional endpoints included LDL-C <1.81 mmol/l, LDL-C reduction ≥50% and other lipids. Exploratory analyses included percentage changes in fasting and post mixed-meal tolerance test (MMTT) lipoproteins and lipids, glucose metabolism variables and inflammatory biomarkers.

RESULTS

In total, 421 individuals were randomised and analysed, having received evolocumab (280 participants) or placebo (141 participants) (mean [SD] age 62 [8] years; 44% women; 77% white). Evolocumab decreased LDL-C by 54.3% (1.4%) at week 12 (vs 1.1% [1.9%] decrease with placebo; p < 0.0001) and by 65.0% (1.3%) at the mean of weeks 10 and 12 (vs 0.8% [1.8%] decrease with placebo; p < 0.0001); it also decreased non-HDL-cholesterol (HDL-C) by 46.9% (1.3%) at week 12 (vs 0.6% [1.8%] decrease with placebo) and by 56.6% (1.2%) at the mean of weeks 10 and 12 (vs 0.1% [1.6%] decrease with placebo). Evolocumab significantly improved levels of other lipids and allowed more participants to reach LDL-C <1.81 mmol/l or a reduction in LDL-C levels ≥50%. After an MMTT (120 min), there were favourable changes (p < 0.05; nominal, post hoc, no multiplicity adjustment) in chylomicron triacylglycerol (triglycerides), chylomicron cholesterol, VLDL-C and LDL-C. Evolocumab had no effect on glycaemic variables and was well tolerated.

CONCLUSIONS/INTERPRETATION

In statin-treated individuals with type 2 diabetes and hypercholesterolaemia or mixed dyslipidaemia, evolocumab significantly reduced LDL-C and non-HDL-C. Favourable changes (p < 0.05) were observed in postprandial levels of chylomicrons, VLDL-C and LDL-C.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02739984 FUNDING: This study was funded by Amgen Inc.

DATA AVAILABILITY

Qualified researchers may request data from Amgen clinical studies. Complete details are available at www.amgen.com/datasharing .

Metabolomic consequences of genetic inhibition of PCSK9 compared with statin treatment

Background

Both statins and PCSK9 inhibitors lower blood low-density lipoprotein cholesterol (LDL-C) levels to reduce risk of cardiovascular events. To assess potential differences between metabolic effects of these two lipid-lowering therapies, we performed detailed lipid and metabolite profiling of a large randomized statin trial and compared the results with the effects of genetic inhibition of PCSK9, acting as a naturally occurring trial.

Methods

228 circulating metabolic measures were quantified by nuclear magnetic resonance spectroscopy, including lipoprotein subclass concentrations and their lipid composition, fatty acids, and amino acids, for 5,359 individuals (2,659 on treatment) in the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) trial at 6-months post-randomization. The corresponding metabolic measures were analyzed in eight population cohorts (N=72,185) using PCSK9 rs11591147 as an unconfounded proxy to mimic the therapeutic effects of PCSK9 inhibitors.

Results

Scaled to an equivalent lowering of LDL-C, the effects of genetic inhibition of PCSK9 on 228 metabolic markers were generally consistent with those of statin therapy (R2=0.88). Alterations in lipoprotein lipid composition and fatty acid distribution were similar. However, discrepancies were observed for very-low-density lipoprotein (VLDL) lipid measures. For instance, genetic inhibition of PCSK9 had weaker effects on lowering of VLDL-cholesterol compared with statin therapy (54% vs. 77% reduction, relative to the lowering effect on LDL-C; P=2x10-7 for heterogeneity). Genetic inhibition of PCSK9 showed no significant effects on amino acids, ketones, or a marker of inflammation (GlycA) whereas statin treatment weakly lowered GlycA levels.

Conclusions

Genetic inhibition of PCSK9 had similar metabolic effects to statin therapy on detailed lipid and metabolite profiles. However, PCSK9 inhibitors are predicted to have weaker effects on VLDL lipids compared with statins for an equivalent lowering of LDL-C, which potentially translate into smaller reductions in cardiovascular disease risk.