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

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.

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.

HDL as a target in the treatment of atherosclerotic cardiovascular disease

Lipid abnormalities are among the key risk factors for cardiovascular disease. Indeed, lipid-modifying drugs - in particular, the statins, which primarily lower plasma levels of low-density lipoprotein (LDL) cholesterol - considerably reduce the risk of cardiovascular events, leading to their widespread use. Nevertheless, it seems that there might be limits to the degree of benefit that can be achieved by lowering LDL-cholesterol levels alone, which has led to increased interest in targeting other lipid-related risk factors for cardiovascular disease, such as low levels of high-density lipoprotein (HDL) cholesterol. In this article, we first consider the mechanisms that underlie the protective effect of HDL cholesterol, and then discuss several strategies that have recently emerged to increase levels of HDL cholesterol to treat cardiovascular disease, including nuclear receptor modulation, inhibition of cholesteryl ester transfer protein and infusion of apolipoprotein/phospholipid complexes.

Lipoprotein(a): an emerging cardiovascular risk factor

Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.

Inhibition of apolipoprotein(a) synthesis in cynomolgus monkey hepatocytes by retinoids via involvement of the retinoic acid receptor

We have shown previously that retinoids induce apolipoprotein (apo) A-I gene expression in cultured cynomolgus hepatocytes and do not have an effect on apo B-100 synthesis. In the present study, the effect of retinoids on apolipoprotein(a) (apo(a)) synthesis in cultured hepatocytes was investigated. The addition of all-trans retinoic acid (at-RA) to the medium of the hepatocytes resulted in a dose- and time-dependent decrease in apo(a) synthesis. Maximal inhibition was 54% after 72 hr of incubation with 10 micromol/L at-RA. Apo B-100 synthesis remained constant, while apo A-I synthesis was increased by 112% after treatment with 10 micromol/L at-RA for 72 hr, indicating that at-RA does not have a general effect on apolipoprotein synthesis in hepatocytes. 9-cis-RA (-36%) and 13-cis-RA (-20%) also inhibited apo(a) synthesis, whereas retinol was not active. To investigate which retinoid receptors are involved in the inhibition of apo(a) synthesis, specific retinoid X receptor (RXR) and retinoic acid receptor (RAR) ligands were used. 4-[1-(3,5,5,8,8-Pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-ethenyl] benzoic acid (3-methyl-TTNEB), a specific RXR agonist, did not have an effect on apo(a) synthesis, whereas incubation with (E)-4-[2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthalenyl)-1-prope nyl] benzoic acid (TTNPB), a specific RAR agonist, resulted in a decrease of 34%. Steady-state apo(a) mRNA levels were decreased by 42% and 33% after the cells were incubated for 48 hr with 10 micromol/L at-RA and TTNPB, respectively, indicating that the decreased synthesis is regulated at the (post)transcriptional level. We conclude that retinoids down-regulate apo(a) synthesis and mRNA via involvement of RAR and not the RXR homodimer in cynomolgus hepatocytes.