Effect of gemfibrozil on levels of lipoprotein[a] in type II hyperlipoproteinemic subjects

Lipoprotein (a): gene genie

PURPOSE OF REVIEW

Despite being both the longest known and the most prevalent genetic risk marker for atherosclerotic cardiovascular disease (CVD), little progress has been made in agreeing a role for lipoprotein (a) [Lp(a)] in clinical practice and developing therapies with specific Lp(a)-lowering activity. We review barriers to progress, and discuss areas of controversy which are important to future research.

RECENT FINDINGS

Epidemiological and genetic studies have supported a causal role for Lp(a) in accelerated atherosclerosis, independent of other risk factors. Progress continues to be made in the understanding of Lp(a) metabolism, and Lp(a) levels, rather than apolipoprotein (a) isoform size, have been shown to be more closely related to CVD risk. Selective Lp(a) apheresis has offered some evidence that Lp(a)-lowering can improve cardiovascular end-points.

SUMMARY

We have acquired a great deal of knowledge about Lp(a), but this has not yet led to reductions in CVD. This is at least partially due to disagreement over Lp(a) measurement methodologies, its physiological role and the importance of the elevations seen in renal diseases, diabetes mellitus and familial hypercholesterolaemia. Renewed focus is required to bring assays into clinical practice to accompany new classes of therapeutic agents with Lp(a)-lowering effects.

AMG145, a Monoclonal Antibody Against Proprotein Convertase Subtilisin Kexin Type 9, Significantly Reduces Lipoprotein(a) in Hypercholesterolemic Patients Receiving Statin Therapy

Background—

Lipoprotein(a) [Lp(a)] is an emerging risk factor for cardiovascular disease. Currently, there are few available therapies to lower Lp(a). We sought to evaluate the impact of AMG145, a monoclonal antibody against proprotein convertase subtilisin kexin type 9 (PCSK9), on Lp(a).

Methods and Results—

As part of the LDL-C Assessment With PCSK9 Monoclonal Antibody Inhibition Combined With Statin Therapy (LAPLACE)–Thrombolysis in Myocardial Infarction (TIMI) 57 trial, 631 patients with hypercholesterolemia receiving statin therapy were randomized to receive AMG145 at 1 of 3 different doses every 2 weeks or 1 of 3 different doses every 4 weeks versus placebo. Lp(a) and other lipid parameters were measured at baseline and at week 12. Compared with placebo, AMG145 70 mg, 105 mg, and 140 mg every 2 weeks reduced Lp(a) at 12 weeks by 18%, 32%, and 32%, respectively ( P <0.001 for each dose versus placebo). Likewise, AMG145 280 mg, 350 mg, and 420 mg every 4 weeks reduced Lp(a) by 18%, 23%, and 23%, respectively ( P <0.001 for each dose versus placebo). The reduction in Lp(a) correlated with the reduction in low-density lipoprotein cholesterol (ρ=0.33, P <0.001). The effect of AMG145 on Lp(a) was consistent regardless of age, sex, race, history of diabetes mellitus, and background statin regimen. Patients with higher levels of Lp(a) at baseline had larger absolute reductions but comparatively smaller percent reductions in Lp(a) with AMG145 compared with those with lower baseline Lp(a) values.

Conclusions—

AMG145 significantly reduces Lp(a), by up to 32%, among subjects with hypercholesterolemia receiving statin therapy, offering an additional, complementary benefit beyond robust low-density lipoprotein cholesterol reduction with regard to a patient’s atherogenic lipid profile.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01380730.

Therapeutic effects of fibrates in postprandial lipemia

Hypertriglyceridemia is observed in many metabolic diseases such as the metabolic syndrome, diabetes mellitus, or mixed dyslipidemia frequently leading to premature coronary heart disease (CHD). Additionally, several studies have shown that postprandial hypertriglyceridemia is pronounced in patients with CHD, metabolic syndrome, hypertension, and other pathologic conditions. The triglyceride-rich lipoprotein remnants accumulating in the postprandial state seem to be involved in atherogenesis and in events leading to thrombosis. Since abnormal postprandial lipemia is associated with pathologic conditions, its treatment is of clinical importance.Fibrates are of significant help in managing hypertriglyceridemia. This review summarizes the effect of fibric acid derivatives on postprandial lipemia. Fibrates decrease the production of and enhance the catabolism of triglyceride-rich lipoproteins through the activation of peroxisome proliferator-activated receptor-alpha. Results of clinical studies with fibrates have confirmed their action in decreasing postprandial triglyceride levels by increasing lipoprotein lipase activity, decreasing apolipoprotein CIII production, and by increasing fatty acid oxidation in the liver.It is concluded that fibrates are effective agents in lowering the postprandial increase in remnant lipoprotein particles and retinyl palmitate. Furthermore, fibrates can also affect the postprandial lipid profile by increasing hepatic lipase levels and in some cases, by reducing cholesterol ester transfer protein activity. The main target of fibrate therapy is to improve fasting hypertriglyceridemia, which is an essential component associated with improving postprandial lipemia. Fibrates are well tolerated by patients and adverse effects have been reported rarely after their administration.

Effect of Fenofibrate on Lipoprotein(a) in Hypertriglyceridemic Patients

We investigated the effect of fenofibrate on lipoprotein(a)levels in hypertriglyceridemic patients and the parameters relating to its effect. Patients with a triglyceride level >/=300 mg/dL or with a triglyceride level >/=200 mg/dL and a high density lipoprotein cholesterol level </=40 mg/dL were treated either with 200 mg of fenofibrate(Fenofibrate group, n = 56) or with general measures (Control group,n = 56). Lipid and lipoprotein levels were measured at baseline and 2 months. Baseline lipoprotein(a) levels were negatively correlated with triglyceride (r = 20.30, P = 0.001) and alanine aminotransferase levels (r = 20.24, P = 0.012). Fenofibrate therapy increased lipoprotein(a) level from 9.4 6 10.6 to 15.6 6 17.5 mg/dL (P = 0.000). The more triglyceride levels decreased, the more lipoprotein(a) levels increased in all subjects (r = 20.46, P = 0.000) and in Control (r =20.35, P = 0.008) and Fenofibrate groups (r = 20.35, P = 0.008). Fenofibrate elevated lipoprotein(a) level greater in patients with a normal liver function. When Fenofibrate group was divided into two subgroups according to the degree of percentage change in lipoprotein(a) level, change in triglyceride level and alanine aminotransferase level were independent predictors by forward logistic regression analysis. In summary, fenofibrate therapy increases lipoprotein(a) level,and this elevation is associated with change in triglyceride level and liver function.

Novel serologic markers of cardiovascular risk

New serologic markers of cardiovascular risk continue to be amassed. Among the new markers, C-reactive protein, fibrinogen, and homocysteine have enjoyed the most acceptance, but newer concepts such as inflammatory cytokines, aspirin resistance, and antioxidant deficiency continue to emerge. Traditional cardiac risk factors are able to predict less than half of cardiovascular events, and the new array of markers have added little to clinical practice, with their use and significance remaining unclear. This article analyzes the new serologic markers of risk in light of the mechanistic, epidemiologic, and clinical data collected over the past decade, and in so doing provides a comprehensive understanding of their role.

Reduced LPA expression after peroxisome proliferator-activated receptor alpha (PPARα) activation in LPA-YAC transgenic mice

BACKGROUND:: Apolipoprotein(a) (apo(a)), which is part of the atherogenic lipoprotein Lp(a), shares structural homology with plasminogen (plg). Genes coding for plasminogen (PLG) and apo(a) (LPA) are linked and situated 40kb apart in the telomeric region of the long arm of chromosome 6. LPA is naturally expressed only in primates and hedgehogs. Thus, access to knowledge regarding the mechanism by which LPA expression is regulated is limited due to shortage of appropriate animal models. However, mice transgenic for the human LPA gene have been produced. Lp(a) levels in man are genetically determined and not altered significantly by dietary changes. In contrast, mice transgenic for LPA-yeast artificial chromosome (LPA-YAC) have markedly reduced apo(a) levels after maintenance on a high-fat diet. LPA-YAC carries the 40kb LPA-PLG intergenic region, which includes a putative binding site for peroxisome proliferator-activated receptor alpha (PPARalpha). Therefore, we examined if fibrates, which exert their effect via PPARalpha, could alter LPA expression in transgenic mice. METHODS:: Two LPA transgenic mouse lines with or without the LPA-PLG intergenic region we fed either PPARalpha agonist fenofibrate (FF) or 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (WY 14643) containing diets for 3 weeks. For the study of serum apo(a) levels, blood were sampled prior the experiment and when the animals were sacrificed. For the study of gene expression pattern pieces of livers were collected and submerged in RNAlater buffer and stored at -70 degrees C until analysis by quantitative PCR. RESULTS AND CONCLUSIONS:: The results showed that fibrates reduce LPA expression in LPA-YAC transgenic mice, but have no impact on hepatic apo(a) mRNA or serum apo(a) protein levels in LPA-cDNA transgenic mice, which lack the LPA-PLG intergenic region. This suggests that the effect of fibrates on LPA expression is mediated upstream of the LPA gene. However, on the basis of current data it is not possible to conclude that PPARalpha is the primary factor that represses LPA expression in LPA-YAC transgenic mice. Negative correlation between FXR and apo(a) mRNA levels, in addition to putative FXR DNA binding sequence in LPA-PLG intergenic region, suggest that it is equally likely that reduced expression of LPA could be a secondary consequence of PPARalpha activation on other genes, such as FXR.

Conditional risk factors for atherosclerosis

Although most patients who experience a coronary heart disease (CHD) event have one or more of the conventional risk factors for atherosclerosis, so do many people who have not yet experienced such an event. Therefore, predictive models based on conventional risk factors have a lower than desired accuracy, providing a stimulus to search for new tools to refine CHD risk prediction. In particular, there is intense interest in evaluating circulating biomarkers related to the atherosclerotic process that might add to our ability to better predict CHD risk. One such group of biomarkers was termed conditional risk factors in an American Heart Association/American College of Cardiology statement in 1999. The conditional risk factors include homocysteine, fibrinogen, lipoprotein(a), low-density lipoprotein particle size, and C-reactive protein. This review updates the conditional risk factors. The main focus is on the potential utility of these risk factors, which are currently available to clinicians, in the prediction of CHD risk in asymptomatic persons. The putative mechanisms of risk, available assays, evidence for association with CHD, and the clinical implications thereof are discussed for each of the risk factors.

Novel risk factors for atherosclerosis

In the past several years, evidence has accumulated that factors other than conventional risk factors may contribute to the development of atherosclerosis. Conventional risk factors predict less than one half of future cardiovascular events. Furthermore, conventional risk factors may not have the same causal effect in different ethnic groups in whom novel risk factors may have a role. These newer risk factors for atherosclerosis include homocysteine, fibrinogen, impaired fibrinolysis, increased platelet reactivity, hypercoagulability, lipoprotein(a), small dense low-density lipoprotein cholesterol, and inflammatory-infectious markers. Identification of other markers associated with an increased risk of atherosclerotic vascular disease may allow better insight into the pathobiology of atherosclerosis and facilitate the development of preventive and therapeutic measures. In this review, we discuss the evidence associating these factors in the pathogenesis of atherosclerosis, the mechanism of risk, and the clinical implications of this knowledge.

Novel risk factors for coronary heart disease: emerging connections

In only 50% of cases of coronary heart disease (CHD) is the cause attributable to the established risk factors of hypertension, cigarette smoking, and elevated total and low-density lipoprotein (LDL) cholesterol levels. This finding has led to research examining other markers for CHD that may have a causal link to the atherothrombotic process. Several of these "emerging" risk factors are reviewed in this article: lipoprotein(a); small dense LDL particle size; hyperhomocysteinemia; and inflammatory, infectious, and hemostatic factors. Evaluation of each of these factors includes a review of the epidemiologic evidence, examination of the pathologic mechanism(s) by which the factor might participate in atherothrombosis, and the clinical utility of screening. Finally, and most relevant for the practicing clinician, the following is addressed: Does evidence exist that selective modification of these risk factors is associated with net clinical benefit?

Effect of dietary lipid-lowering drugs upon plasma lipids and egg yolk cholesterol levels of laying hens

To evaluate the effect of lipid-lowering agents upon egg quality, reproductive performance, plasma lipids, and egg yolk cholesterol levels, 30-week-old Shaver laying hens were fed a basal diet (commercial ration) supplemented with 0.1% probucol (PROB), 0.025% gemfibrozil (GEMF), or lovastatin at 0.0005% (LOV1), 0.001% (LOV2), or 0.0015% (LOV3) for a 12-week experimental period. It was observed that the supplementation of the drugs did not impair albumen and shell quality. Hen performance was not adversely affected. The depression in triglyceride concentrations approached statistical significance only in LOV2 (38.5%), and total cholesterol was significantly depressed in LOV2 (36.0%), LOV3 (36.8%), PROB (29.6%), and GEMF (30.4%) treatments. Egg cholesterol content, expressed per gram of yolk, was significant lowered in LOV1 (7.5%) and LOV3 (12. 7%).

No effect of fibrates on synthesis of apolipoprotein(a) in primary cultures of cynomolgus monkey and human hepatocytes: apolipoprotein A-I synthesis increased

Fibrates have been shown to decrease plasma levels of triglyceride-rich lipoproteins and LDL and to increase HDL. Data on the effect of fibrates on lipoprotein(a) levels in man are not consistent. Because lp(a) levels in vivo are mainly regulated at synthesis level, we studied the effect of fibrates on the synthesis of apolipoprotein(a) (apo(a)) in primary cultures of cynomolgus monkey and human hepatocytes. Furthermore, we assessed the effect of fibrates on apolipoprotein A-I (apo A-I) synthesis and investigated whether different fibrates have different effects on the apo(a) and apo A-I synthesis. The addition of gemfibrozil to cultures of monkey and human hepatocytes had no effect on apo(a) synthesis, but resulted in a dose- and time-dependent increase of apo A-I synthesis and mRNA. In simian hepatocytes maximal stimulation was 2.5-fold after incubation for 72 h with 1.0 mM gemfibrozil, whereas apo A-I synthesis was induced 1.8- and 2.0-fold by using 0.1 mM and 0.3 mM, respectively. Similar results were obtained by using human hepatocytes; apo(a) synthesis remained unchanged, while apo A-I secretion was 2.0-fold increased at 1 mM gemfibrozil. Other fibrates like bezafibrate, clofibrate and clofibric acid did not change apo(a) synthesis either. In contrast, they enhanced the synthesis of apo A-I (1.5-, 1.8- and 1.8-fold, respectively), although less potently than gemfibrozil. We conclude that fibrates have no effect on apolipoprotein(a) synthesis in monkey and human hepatocytes and that these drugs induce apo A-I synthesis.

Peroxisome proliferators and peroxisome proliferator activated receptors (PPARs) as regulators of lipid metabolism

Peroxisome proliferation (PP) in mammalian cells, first described 30 years ago, represents a fascinating field of modern research. Major improvements made in its understanding were obtained through basic advances that have opened up new areas in cell biology, biochemistry and genetics. A decade after the first report on PP, a new metabolic pathway (peroxisomal beta-oxidation) and its inducibility by peroxisome proliferators were discovered. More recently, a new type of nuclear receptor, the peroxisome proliferator-activated receptor (PPAR), has been described. The first PPAR was discovered in 1990. Since then, many other PPARs have been characterized. This original class of nuclear receptors belongs to the superfamily of steroid receptors. With activation of cell signal transduction pathways, the occurrence of PPARs provides, for the first time, a coherent explanation of mechanisms by which PP is triggered. Nevertheless, although many compounds or metabolites are capable of activating PPARs, the natural direct ligands of these receptors have not been, up to now, clearly identified, with, however, the exception of 15-deoxy-12,14-prostaglandin J2 which is the ligand of PPAR gamma 2 while leukotrien LTB4 binds PPAR alpha. At this stage, the hypothesis of some orphan PPARs (ie receptors without known ligand) can not be ruled out. Despite these relatively restrictive aspects, the mechanisms by which activation of PPARs leads to PP become clear; also, coherent hypotheses among which a scenario involving receptor phosphorylation or a heat shock protein (ie HSP 72) can be proposed to explain how PPARs would be activated. The aim of this note is to review recent developments on PPARs, to present members up to now recognized to belong to the PPAR family, their characterization, functions, regulation and mechanisms of activation as well as their involvement in lipid metabolism regulation such as control of beta-oxidation, ketogenesis, fatty acid synthesis and lipoprotein metabolism. As an introducing section, a brief review of the major events between the first report of PP in mammals and the discovery of the first PPAR is given. Another section is devoted to current hypotheses on mechanisms responsible for PPAR activation and PP induction. Rather than an exhaustive presentation of cellular alterations accompanying PP induction, a dynamic overview of the lipid metabolism is provided. By assessing the biological significance of this organellar proliferative process, the reader will be led to conclude that the discovery of PPARs and related gene activation through peroxisome proliferator responsive element (PPRE) makes PP induction one of the most illustrative examples of control that occurs in lipid metabolism.