Fibrate-modulated Expression of Fibrinogen, Plasminogen Activator Inhibitor-1 and Apolipoprotein A-I in Cultured Cynomolgus Monkey Hepatocytes

Cardiovascular-renal complications and the possible role of plasminogen activator inhibitor: a review

Since angiotensin increases the expression of plasminogen activator inhibitor (PAI), mechanisms associated with an actively functioning renin–angiotensin–aldosterone system can be expected to be associated with increased PAI-1 expression. These mechanisms are present not only in common conditions resulting in glomerulosclerosis associated with aging, diabetes or genetic mutations, but also in autoimmune disease (like scleroderma and lupus), radiation injury, cyclosporine toxicity, allograft nephropathy and ureteral obstruction. While the renin–angiotensin–aldosterone system and growth factors, such as transforming growth factor-beta (TGF-β), are almost always part of the process, there are rare experimental observations of PAI-1 expression without their interaction. Here we review the literature on PAI-1 and its role in vascular, fibrotic and oxidative injury as well as work suggesting potential areas of intervention in the pathogenesis of multiple disorders.

Hydrogen Sulfide Up-Regulates the Expression of ATP-Binding Cassette Transporter A1 via Promoting Nuclear Translocation of PPARα

ATP binding cassette transporter A1 (ABCA1) plays a key role in atherogenesis. Hydrogen sulfide (H₂S), a gasotransmitter, has been reported to play an anti-atherosclerotic role. However, the underlying mechanisms are largely unknown. In this study we examined whether and how H₂S regulates ABCA1 expression. The effect of H₂S on ABCA1 expression and lipid metabolism were assessed in vitro by cultured human hepatoma cell line HepG2, and in vivo by ApoE^−/− mice with a high-cholesterol diet. NaHS (an exogenous H₂S donor) treatment significantly increased the expression of ABCA1, ApoA1, and ApoA2 and ameliorated intracellular lipid accumulation in HepG2 cells. Depletion of the endogenous H₂S generator cystathionine γ-lyase (CSE) by small RNA interference (siRNA) significantly decreased the expression of ABCA1 and resulted in the accumulation of lipids in HepG2 cells. In vivo NaHS treatment significantly reduced the serum levels of total cholesterol (TC), triglycerides (TG), and low-density lipoproteins (LDL), diminished atherosclerotic plaque size, and increased hepatic ABCA1 expression in fat-fed ApoE^−/− mice. Further study revealed that NaHS upregulated ABCA1 expression by promoting peroxisome proliferator-activated receptor α (PPARα) nuclear translocation. H₂S up-regulates the expression of ABCA1 by promoting the nuclear translocation of PPARα, providing a fundamental mechanism for the anti-atherogenic activity of H₂S. H₂S may be a promising potential drug candidate for the treatment of atherosclerosis.

Studies in mice, hamsters, and rats demonstrate that repression of hepatic apoA-I expression by taurocholic acid in mice is not mediated by the farnesoid-X-receptor

It is claimed that apoA-I expression is repressed in mice by cholic acid (CA) and its taurine conjugate, taurocholic acid (TCA) via farnesoid X receptor (FXR) activation. We measured apoA-I expression in mice, hamsters, and rats treated with highly potent and selective synthetic FXR agonists or with TCA. All of the synthetic agonists bound to FXR with high affinity in a scintillation proximity assay. However, TCA did not compete with the radioligand up to the highest concentration used (100 μM). The C-site regulatory region of apoA-I, through which FXR has been reported to regulate its expression, is completely conserved across the species investigated. In both male and female human apoA-I-transgenic mice, we reproduced the previously reported strong inhibition of human apoA-I expression upon treatment with the typical supraphysiological dose of TCA used in such studies. However, in contrast to some previous reports, TCA did not repress murine apoA-I expression in the same mice. Also, more-potent and -selective FXR agonists did not affect human or murine apoA-I expression in this model. In LDL receptor-deficient mice and Golden Syrian hamsters, selective FXR agonists did not affect apoA-I expression, whereas in Wistar rats, some even increased apoA-I expression. In conclusion, selective FXR agonists do not repress apoA-I expression in rodents. Repression of human apoA-I expression by TCA in transgenic mice is probably mediated through FXR-independent mechanisms.

Role of the nuclear receptors HNF4 alpha, PPAR alpha, and LXRs in the TNF alpha-mediated inhibition of human apolipoprotein A-I gene expression in HepG2 cells

The expression of the apolipoprotein A-I gene (apoA-I) in hepatocytes is repressed by pro-inflammatory cytokines such as IL-1beta and TNFalpha. In this work, we have demonstrated that treatment of HepG2 human hepatoma cells with chemical inhibitors for JNK, p38 protein kinases, and NFkappaB transcription factor abolishes the TNFalpha-mediated inhibition of human apoA-I gene expression in HepG2 cells. In addition, we have shown that TNFalpha decreases also the rate of secretion of apoA-I protein by HepG2 cells, and this effect depends on JNK and p38, but not on NFkappaB and MEK1/2 signaling pathways. The inhibitory effect of TNFalpha has been found to be mediated by the hepatic enhancer of the apoA-I gene. The decrease in the level of human apoA-I gene expression under the impact of TNFalpha appears to be partly mediated by the inhibition of HNF4alpha and PPARalpha gene expression. Treatment of HepG2 cells with PPARalpha antagonist (MK886) or LXR agonist (TO901317) abolishes the TNFalpha-mediated decrease in the level of apoA-I gene expression. PPARalpha agonist (WY-14643) abolishes the negative effect of TNFalpha on apoA-I gene expression in the case of simultaneous inhibition of MEK1/2, although neither inhibition of MEK1/2 nor addition of WY-14643 leads to the blocking of the TNFalpha-mediated decrease in the level of apoA-I gene expression individually. The ligand-dependent regulation of apoA-I gene expression by PPARalpha appears to be affected by the TNFalpha-mediated activation of MEK1/2 kinases, probably through PPARalpha phosphorylation. Treatment of HepG2 cells with PPARalpha and LXR synthetic agonists also blocks the inhibition of apoA-I protein secretion in HepG2 cells under the impact of TNFalpha. A chromatin immunoprecipitation assay demonstrates that TNFalpha leads to a 2-fold decrease in the level of PPARalpha binding with the apoA-I gene hepatic enhancer. At the same time, the level of LXRbeta binding with the apoA-I gene hepatic enhancer is increased 3-fold under the impact of TNFalpha. These results suggest that nuclear receptors HNF4alpha, PPARalpha, and LXRs are involved in the TNFalpha-mediated downregulation of human apoA-I gene expression and apoA-I protein secretion in HepG2 cells.

Differentiated CaCo-2 cells as an in-vitro model to evaluate de-novo apolipoprotein A-I production in the small intestine

BACKGROUND

Increasing HDL cholesterol concentrations by stimulating de-novo apolipoprotein A-I (apoA-I) production in the liver and/or in the small intestine is a potential strategy to reduce coronary heart disease risk. Although there is quite some knowledge concerning regulatory effects in the liver, less is known concerning potential agents that could elevate de-novo apoA-I production in the small intestine.

METHODS

Therefore, we compared side-by-side effects of various peroxisome proliferator-activated receptor (PPAR)alpha, PPARgamma, retinoid-X-receptor alpha, and farnesoid-X-receptor agonists on de-novo apoA-I production in differentiated CaCo-2 and HepG2 cells.

RESULTS

For PPARa agonists, we showed that GW7647 elevated apoA-I concentrations in the medium of both cell models, whereas WY14643 elevated only de-novo apoA-I concentrations in differentiated CaCo-2 cells. Unexpectedly, fenofibric acid lowered apoA-I medium concentrations in both cell lines, which could not be explained by a lack of PPAR transactivation or a lack of retinoid-X-receptor a activation. For farnesoid-X-receptor agonists, chenodeoxycholic acid strongly reduced apoA-I concentrations both in differentiated CaCo-2 and HepG2 cells, whereas GW4064 and taurocholate only lowered apoA-I in CaCo-2 cells (GW4064) or in HepG2 cells (taurocholate). However, overall effects of all individual components on apoA-I production in differentiated CaCo-2 and HepG2 cells were highly correlated (r = 0.68; P = 0.037; N=9).

CONCLUSION

We conclude that differentiated CaCo-2 cells are suitable models to study de-novo small intestinal apoA-I production in vitro enabling the possibility to screen for potential bioactive dietary components. This cell model may also determine small-intestinal-specific effects, as some discrepancy was found between both cell models.

Renoprotective effects of fenofibrate in diabetic rats are achieved by suppressing kidney plasminogen activator inhibitor-1

To investigate mechanisms of protective effects of fenofibrate on the diabetic kidney, male Wistar rats were divided into control, untreated diabetes, and fenofibrate-treated (32 mg kg(-1) d(-1), 8 weeks) diabetes groups. Diabetes induced by streptozotocin (25 mg/kg) and a high-fat diet was characterized by the disorders of plasma glucose and lipids. In untreated diabetic rats, there were increases in glomerular volume, matrix content, expressions of laminin and urinary albumin excretion. These nephropathies were associated with the upregulations of plasminogen activator inhibitor 1 (PAI-1) mRNA expression and its protein activity in the renal cortex, and a significant increase in transforming growth factor beta1 (TGF-beta1) expression. Treatment with fenofibrate suppressed the expression of PAI-I mRNA and its protein activity, and inhibited TGF-beta1 overexpression. It also partially reversed metabolic disorders and pathophysiologic changes associated with diabetic nephropathy. Our results indicate that fenofibrate delays the progression of diabetic nephropathy in rats to some extent. These renoprotective effects are likely to be achieved through suppression of PAI-1 and TGF-beta1 in the renal cortex, and consequently less extracellular matrix deposition.

Fenofibrate: a novel formulation (Triglide) in the treatment of lipid disorders: a review

Cardiovascular disease is the major cause of mortality worldwide and accounts for approximately 40% of all deaths. Dyslipidemia is one of the primary causes of atherosclerosis and effective interventions to correct dyslipidemia should form an integral component of any strategy aimed at preventing cardiovascular disease. Fibrates have played a major role in the treatment of hyperlipidemia for more than two decades. Fenofibrate is one of the most commonly used fibrates worldwide. Since fenofibrate was first introduced in clinical practice, a major drawback has been its low bioavailability when taken under fasting conditions. Insoluble Drug Delivery-Microparticle fenofibrate is a new formulation that has an equivalent extent of absorption under fed or fasting conditions. In this review, we will discuss the clinical pharmacology of fenofibrate, with particular emphasis on this novel formulation, as well as its lipid-modulating and pleiotropic actions. We will also analyze the major trial that evaluated fibrates for primary and secondary prevention of cardiovascular disease, the safety and efficacy profile of fibrate-statin combination treatment, and the current recommendations regarding the use of fibrates in clinical practice.

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.

Characterization of a small molecule PAI-1 inhibitor, ZK4044

Plasminogen activator inhibitor-1 (PAI-1) is a key negative regulator of the fibrinolytic system. In animal studies, inhibition of PAI-1 activity prevents arterial and venous thrombosis, indicating that PAI-1 inhibitors may be used as a new class of antithrombotics. In this study, we characterize a small molecule PAI-1 inhibitor, ZK4044, which was identified by high throughput screening and chemically optimized. In a chromogenic substrate-based urokinse (uPA)/PAI-1 assay and a tissue-type plasminogen activator (tPA)-mediated clot lysis assay, ZK4044 inhibited human PAI-1 activity with IC50 values of 644+/-255 and 100+/-90 nM, respectively. ZK4044 had no detectable inhibitory activity toward other serpins such as antithrombin III, alpha1-antitrypsin and alpha2-antiplasmin, indicating that ZK4044 is a specific PAI-1 inhibitor. ZK4044 was shown to bind directly to PAI-1 and prevent the binding of PAI-1 to tPA in a dose-dependent manner in surface plasmon resonance Biacore-based experiments. ZK4044 also prevented PAI-1/tPA complex formation, as analyzed by SDS/PAGE. ZK4044 had little effect on elastase-mediated cleavage of active PAI-1, indicating that the primary mode of action of ZK4044 is most likely to directly block the PAI-1/tPA interaction rather than to convert active PAI-1 to latent PAI-1. In the chromogenic substrate-based uPA/PAI-1 assay, ZK4044 was approximately 2-fold less potent against a mutant PAI-1 (14B-1), which contains four mutations at N150H, K154T, Q319L and M354I, compared with wild-type PAI-1, suggesting that the ZK4044 binding site on the surface of PAI-1 is close to these mutant residues. Together, our data show that ZK4044 represents a new class of small molecule PAI-1 inhibitors with anti-thrombotic potential.

The Protein Kinase C Signaling Pathway Regulates a Molecular Switch between Transactivation and Transrepression Activity of the Peroxisome Proliferator-Activated Receptor α

Peroxisome proliferator-activated receptor (PPAR) alpha is a nuclear receptor implicated in several physiological processes such as lipid and lipoprotein metabolism, glucose homeostasis, and the inflammatory response. PPARalpha is activated by natural fatty acids and synthetic compounds like fibrates. PPARalpha activity has been shown to be modulated by its phosphorylation status. PPARalpha is phosphorylated by kinases such as the MAPKs and cAMP-activated protein kinase A. In this report, we show that protein kinase C (PKC) inhibition impairs ligand-activated PPARalpha transcriptional activity. Furthermore, PKC inhibition decreases PPARalpha ligand-induction of its target genes including PPARalpha itself and carnitine palmitoyltransferase I. By contrast, PKC inhibition enhances PPARalpha transrepression properties as demonstrated using the fibrinogen-beta gene as model system. Finally, PKC inhibition decreases PPARalpha phosphorylation activity of hepatocyte cell extracts. In addition, PPARalpha purified protein is phosphorylated in vitro by recombinant PKCalpha and betaII. The replacement of serines 179 and 230 by alanine residues reduces the phosphorylation of the PPARalpha protein. The PPARalpha S179A-S230A protein displays an impaired ligand-induced transactivation activity and an enhanced trans-repression activity. Altogether, our data indicate that the PKC signaling pathway acts as a molecular switch dissociating the transactivation and transrepression functions of PPARalpha, which involved phosphorylation of serines 179 and 230.

The hypolipidemic drug metabolites nafenopin-CoA and ciprofibroyl-CoA are competitive P2Y1 receptor antagonists

Coenzyme A (CoA-SH), endogenous and drug-derived CoA-derivatives were tested as putative antagonists of P2Y receptors expressed in Xenopus laevis oocytes, a method used to determine calcium-activated chloride current, an indicator of the activation of these receptors. CoA-SH antagonized reversibly and in a concentration-dependent manner the ATP-gated currents evoked by the human P2Y(1) but not the P2Y(2) receptor. Palmitoyl-CoA was four-fold more potent than CoA-SH as an antagonist while palmitoyl-carnitine was inactive, highlighting the role of the CoA-SH moiety in the antagonism. The CoA derivatives of nafenopin and ciprofibrate, two clinically relevant hypolipidemic drugs, increased 13 and three-fold the potency of CoA-SH, respectively. The K(B)s of nafenopin-CoA and ciprofibroyl-CoA were 58 and 148 nM, respectively; the slopes of the Schild plots were unitary. Neither 100 microM nafenopin nor ciprofibrate alone altered the P2Y(1) receptor activity. Neither CoA-SH nor ciprofibroyl-CoA antagonized the rat P2X(2) or the P2X(4) nucleotide receptors nor interacted with the 5-HT(2A/C) receptors. The bulky drug CoA-SH derivatives identify a hydrophobic pocket, which may serve as a potential target for novel selective P2Y(1) antagonists.

Effect of ciprofibrate on lipoproteins, fibrinogen, renal function, and hepatic enzymes

AIM

The action of ciprofibrate in hypertriglyceridemic patients is well established. Not only is ciprofibrate able to alter the lipid profile, but it can also change the values of fibrinogen, C-reactive protein, creatinine, transaminases, gamma-glutamyl transpeptidase and serum alkaline phosphatase. However, previous studies focused on the effect of ciprofibrate in hypertriglyceridemic patients, leaving unanswered the question of whether ciprofibrate exerts the same effect on hyperlipidemic patients with normal triglyceride values. The aim of this study is to answer this question.

METHODS

In this randomized clinical trial, 64 men and women with elevated cholesterol or triglyceride levels were included. Two subgroups were formed according to triglyceride levels: one (36 patients) with elevated triglyceride levels (> 200 mg/dL [2.26 mmol/L]) and another (28 patients) with normal triglyceride levels (< 200 mg/dL [2.26 mmol/l]). After a 6-week period of step 1 diet according to the National Cholesterol Education Program, ciprofibrate (100 mg once daily) was administered for 16 weeks. Primary efficacy points were the changes of lipid parameters (total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglycerides, apoproteins A1, B, E and lipoprotein [a], high sensitivity C reactive protein, fibrinogen, glucose, insulin, aspartate transaminase, alanine transaminase, gamma-glutamyl transpeptidase, alkaline phosphatase, urea and creatinine levels in a fasting blood sample before and after treatment with ciprofibrate.

RESULTS

The subgroup with triglyceride < 200 mg/dL (2.26 mmol/L): After the administration of ciprofibrate total cholesterol and low-density lipoprotein cholesterol were reduced by 15% (P < 0.001), and 19% (P < 0.001), respectively, while high-density lipoprotein cholesterol increased by 9% (P = 0.02). Apoproteins B and E levels were reduced by 21% (P < 0.001) and 11% (P = 0.002), respectively. Subgroup with triglyceride > 200 mg/dL (2.26 mmol/L): After the administration of ciprofibrate, no significant change in LDL cholesterol levels was observed. Total cholesterol levels were reduced by 15% (P < 0.001) and high-density lipoprotein cholesterol levels were increased by 13% (P = 0.004). Apoprotein B and apoprotein E levels were reduced by 16% (P < 0.001) and 30% (P < 0.001), respectively. Apoprotein-A1 levels were increased by 5% (P = 0.024). In the whole group of patients, the fibrinogen levels fell by 7% (P = 0.043), and the serum creatinine level increased by 10% (P < 0.001). This rise in serum creatinine was more pronounced in patients with low triglyceride levels (15% vs 5%, P = 0.009). Ciprofibrate decreased C-reactive protein levels by 26% in 44 patients who had C-reactive protein measurements (P < 0.001). gamma-glutamyl transpeptidase activity was similarly decreased (by approximately 40%) in both groups of patients. Alkaline phosphatase activity decreased in both groups, a reduction which was greater in hypertriglyceridemics (20% vs 10%, P = 0.004).

CONCLUSIONS

Ciprofibrate improved some of the vascular risk factors, such as total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apoproteins A1, B, and E, and fibrinogen levels in both hypertriglyceridemics and normotriglyceridemics. In addition, ciprofibrate raised the serum creatinine and improved the activity of the hepatic enzymes in the plasma in both patient subgroups.

Genetic determinants of the response to bezafibrate treatment in the lower extremity arterial disease event reduction (LEADER) trial

Genetic determinants of baseline levels and the fall in plasma triglyceride and fibrinogen levels in response to bezafibrate treatment were examined in 853 men taking part in the lower extremity arterial disease event reduction (LEADER) trial. Three polymorphisms in the peroxisome proliferator activated receptor alpha (PPARalpha) gene were investigated (L162V, G>A in intron 2 and G>C in intron 7), two in the apolipoprotein CIII (APOC3) gene (-482C>T and -455T>C) and one in the beta-fibrinogen (FIBB) gene (-455G>A). The presence of diabetes (n=158) was associated with 15% higher triglyceride levels at baseline compared to non-diabetics (n=654) (P<0.05). Among the diabetic group, carriers of the PPARalpha intron 7 C allele had 20% lower triglyceride levels compared to homozygotes for the common G allele (P<0.05), with a similar (non-significant) trend for the L162V polymorphism, which is in linkage disequilibrium with the intron 7 polymorphism. For the APOC3 gene, carriers of the -482T allele had 13% lower baseline triglyceride levels compared to -482C homozygotes (P<0.02), but no effect was observed with the -455T>C substitution. In the non-diabetic patients, the PPARalpha V162 allele was significantly associated with 9% higher baseline triglyceride levels (P<0.03) and a similar, but non-significant trend was seen for the intron 7 polymorphism. Overall, triglyceride levels fell by 26% with 3 months of bezafibrate treatment, and current smokers showed a poorer response compared to ex/non-smokers (23% fall compared to 28% P=0.03), but none of the genotypes examined had a significant influence on the magnitude of response. Carriers of the -455A polymorphism of the FIBB gene had, as expected, marginally higher baseline fibrinogen levels, 3.43 versus 3.36 g/l (P=0.055), but this polymorphism did not affect response to treatment. Overall, fibrinogen levels fell by 12%, with patients with the highest baseline fibrinogen levels showing the greatest decrease in response to bezafibrate. For both the intron 2 and the L162V polymorphisms of the PPARalpha gene there was a significant interaction (both P<0.01) between genotype and baseline levels of fibrinogen on the response of fibrinogen levels to bezafibrate, such that individuals carrying the rare alleles in the lowest tertile showed essentially no overall decrease compared to a 0.18 g/l fall in homozygotes for the common allele. Thus while these genotypes are a minor determinant of baseline triglyceride and fibrinogen levels, there is little evidence from this study that the magnitude of response to bezafibrate treatment in men with peripheral vascular disease is determined by variation at these loci.

A pharmacoepidemiological assessment of the effect of statins and fibrates on fibrinogen concentration

Plasma fibrinogen is strongly associated with cardiovascular morbi-mortality. We investigated in the large cohort of the D.E.S.I.R. (data from an epidemiological study on the insulin resistance syndrome) study, the relationship between change in fibrinogen concentration over a 3-year follow-up and fibrate and statin use. Fibrinogen concentrations were higher at baseline among individuals treated with statins (n=130) compared to those treated with fibrates (n=251), even after adjustment for confounding factors (including total cholesterol, HDL cholesterol and triglycerides) (mean (S.D.): 2.8 (0.6) vs. 3.1 (0.6), P<0.001). We compared change in fibrinogen concentrations at 3 years of follow-up, between individuals who started fibrate (n=126) or statin (n=127) treatment during the follow-up and individuals (n=3906) who stayed without treatment during this period. After adjustment for baseline fibrinogen level, age, sex and changes in total cholesterol, triglycerides and alcohol intake, fibrinogen concentration decreased after fibrate treatment, while it increased after statin treatment and in those not using lipid lowering drugs (-0.07 (0.54) vs. 0.10 (0.54) vs. 0.08 (0.52) g/l respectively, P=0.01). No differences were observed between different statins or different fibrates. In conclusion, fibrates in contrast with statins may combine lipid-lowering with a beneficial effect on fibrinogen. This effect is independent of changes in cholesterol and triglyceride concentrations.

Effects of fibrates on serum metabolic parameters

Fibric acid derivatives are a class of hypolipidaemic drugs used in the treatment of patients with hypertriglyceridaemia, mixed hyperlipidaemia and diabetic dyslipidaemia. Fibrate therapy results in a significant decrease in serum triglycerides and an increase in high-density lipoprotein (HDL) cholesterol levels. The latest drugs of this class are also effective in lowering low-density (LDL) cholesterol levels and can change the distribution of LDL towards higher and larger particles. The effects of fibrates on lipid metabolism are mostly mediated through the activation of peroxisome proliferator-activated receptors (PPARalpha). A number of angiographic and clinical trials have confirmed that fibrates can slow the progression of atherosclerotic disease and decrease cardiovascular morbidity and mortality. Recently published data suggest that the ability of fibrates to prevent atherosclerosis is not related only to their hypolipidaemic effects but also to other 'pleiotropic effects', such as their anti-inflammatory, antioxidant and antithrombotic effects, as well as their ability to improve endothelial function. Interestingly, fibrates may favourably influence the thrombotic/fibrinolytic system. In fact, most of these drugs can significantly decrease plasma fibrinogen levels and inhibit tissue factor expression and activity in human monocytes and macrophages. Some studies have shown that fibrates can improve carbohydrate metabolism in patients with dyslipidaemia, including diabetic patients. Among fibrates only fenofibrate can significantly decrease serum uric acid levels by increasing renal urate excretion. Fibrates, with the possible exception of gemfibrozil, can significantly increase serum creatinine and homocysteine levels. Finally, a reduction in serum alkaline phosphatase and gamma glutamyltranspeptidase (gammaGT) activity is a well-documented effect of therapy with fibrates. The fibrates are generally well-tolerated drugs with few side-effects. The most important side-effect is myositis, which is observed in patients with impaired renal function or when statins are given concomitantly.

Current practice in the treatment of hyperlipidaemias

Primary and secondary prevention trials for coronary heart disease (CHD) in hyperlipidaemic or so-called 'normolipidaemic' patients with drugs affecting lipid metabolism have clearly confirmed that even slight alterations in lipoprotein metabolism are major risk factors for CHD. The global cardiovascular risk must be determined before deciding to treat patients with drugs affecting lipid metabolism. Screening for dyslipidaemia consists of determining cholesterol (C), LDL-cholesterol (LDL-C), HDL-cholesterol (HDL-C) and triglyceride (TG) plasma levels and the decision to treat depends mainly on LDL-C plasma levels. Furthermore, secondary dyslipidaemia must be diagnosed and primary disease must be adequately treated. There are four classes of available lipid-regulating drugs: HMG-CoA reductase inhibitors (statins), bile acid sequestrants (resins), peroxisome proliferator-activated receptor-alpha (PPAR- alpha) activators (fibrates) and nicotinic acid. All four will be discussed in this review. Clinical trials have shown that drugs improving lipid metabolism reduce CHD relative risk from 24% (secondary prevention) to 37% (primary prevention) and the absolute risk from 2% (primary prevention) to 8.5% (secondary prevention). These studies indicate that the number of patients needed to be treated to economise one clinical event ranges from 12 (secondary prevention) to 50 (primary prevention). Clinical trials are currently testing the hypothesis that 'lower LDL-C is better'.

PPARS, metabolic disease and atherosclerosis

PPAR-alpha belongs to the family of nuclear receptors. Activated PPAR-alpha stimulates the expression of genes involved in fatty acid and lipoprotein metabolism. PPAR-alpha activators, such as the normolipidaemic fibric acids, decrease triglyceride concentrations by increasing the expression of lipoprotein lipase and decreasing apo C-III concentration. Furthermore, they increase HDL-cholesterol by increasing the expression of apo A-I and apo A-II. PPAR-alpha activation by fibric acids improves insulin sensibility, and decreases thrombosis and vascular inflammation. PPAR-alpha activators (gemfibrozil) decrease the risk of coronary heart disease in patients with normal LDL-cholesterol and low HDL-cholesterol (VA-HIT) and they slow the progression of premature coronary atherosclerosis (BECAIT) (bezafibrate), particularly in patients with type 2 diabetes (DAIS) (fenofibrate).

Effects of diet, drugs, and genes on plasma fibrinogen levels

Plasma levels of fibrinogen have been identified as independent risk predictors of cardiovascular disease. This has greatly increased interest in the regulation of plasma fibrinogen levels. Many demographic and environmental factors are known to affect fibrinogen levels, such as diet, use of several drugs, age, smoking, body mass, gender, physical exercise, race, and season. Additionally, it is also known that genetic factors determine the fibrinogen levels, and also that they determine the response of fibrinogen levels to environmental factors. Estimates, based on twin studies, suggest that 30-50% of the plasma fibrinogen level is genetically determined. The effect of dietary components on plasma fibrinogen levels is modest. Several components have been identified as factors that influence fibrinogen levels. Among those are fish oil, other lipids, and fibers. Dietary components that were expected to have an effect on fibrinogen, but for which no association was observed are black and green tea. Several drugs are known to influence fibrinogen levels, the most studied of which are platelet aggregation inhibiting drugs, such as ticlopidine, and the lipid lowering fibric acid derivatives (fibrates). Both types of drugs decreased the plasma fibrinogen level by about 10%, and bezafibrate lowers fibrinogen even more in patients with diabetes. No clear effect was observed for the HMG-CoA reductase inhibitors (statins). In the Bezalip study, fibrinogen levels decreased in patients treated with bezafibrate, but this had no clear effect on the risk of cardiovascular disease. This suggests that several mechanisms influence the fibrinogen level and that these mechanisms may contribute differently to cardiovascular disease. Several variations in the fibrinogen genes have been described and especially variations in the promoter region of the fibrinogen beta-gene are interesting, because the synthesis of the fibrinogen B beta chain is considered to be the rate limiting step in the fibrinogen biosynthesis. In many studies the fibrinogen beta-gene polymorphisms (-455G/A, -148C/T, and BclI) are found to be associated with the plasma levels of fibrinogen. However, they are not associated with the risk of cardiovascular events, although in several studies an association with the severity and progression of atherosclerosis has been reported. It has also been observed frequently that the fibrinogen beta-gene promoter polymorphisms are associated with the response of fibrinogen levels to environmental factors, such as exercise and trauma. In conclusion, plasma fibrinogen levels are regulated by an interesting and complex interplay between environmental and genetic factors.

The role of fibric acids in atherosclerosis

The hypolipidemic fibric acid drugs are peroxisome proliferator-activated receptor a (PPAR alpha) ligands. PPAR alpha activated by fibric acids form heterodimers with the 9-cis retinoic acid receptor (RXR). The PPAR/RXR heterodimers bind to peroxisome proliferator response elements (PPRE), which are located in numerous gene promoters and increase the level of the expression of mRNAs encoded by PPAR alpha target genes. Fibric acids decrease triglyceride plasma levels through increases in the expression of genes involved in fatty acid-beta oxidation. Furthermore, they decrease triglycerides by increasing lipoprotein lipase gene expression and by decreasing apolipoprotein C-III gene expression. Fibric acids increase high-density lipoprotein (HDL) cholesterol partly by increasing apolipoprotein A-I and apolipoprotein A-II gene expression. Fibric acids also reduce vascular wall inflammation and the expression of genes involved in different vascular functions (ie, vasomotricity, thrombosis). Fibric acids are used to treat primary hypertriglyceridemia and mixed hyperlipidemia. Some fibric acid molecules are active in essential hypercholesterolemia. Clinical evidence shows that fibric acids reduce coronary atherosclerosis progression in dyslipidemic patients (eg, bezafibrate, gemfibrozil) and in type 2 diabetic patients (fenofibrate). Gemfibrozil decreases coronary morbidity and mortality in patients with low HDL cholesterol, normal triglycerides,and normal low-density lipoprotein (LDL) cholesterol plasma levels. Further clinical studies are necessary to investigate if fibric acids decrease cardiovascular mortality in type 2 diabetes and in primary prevention of hypertriglyceridemia and hypolipidemia.

Activation of human peroxisome proliferator-activated receptor (PPAR) subtypes by pioglitazone

Pioglitazone, a thiazolidinedione (TZD) derivative, is an antidiabetic agent that improves hyperglycaemia and hyperlipidaemia in obese and diabetic animals via a reduction in hepatic and peripheral insulin resistance. The TZDs including pioglitazone have been identified as high affinity ligands for peroxisome proliferator-activated receptor (PPAR) gamma. The selectivity of pioglitazone for the human PPAR subtypes has not been reported, thus, we investigated the effect of pioglitazone on the human PPAR subtypes. Transient transactivation assay showed that pioglitazone is a selective hPPARgamma1 activator and a weak hPPARalpha activator. Binding assay indicated that the transactivation of hPPARgamma1 or hPPARalpha by pioglitazone is due to direct binding of pioglitazone to each subtype. Furthermore, pioglitazone significantly increased the apoA-I secretion from the human hepatoma cell line HepG2.

Effect of micronized fenofibrate on plasma lipoprotein levels and hemostatic parameters of hypertriglyceridemic patients with low levels of high-density lipoprotein cholesterol in the fed and fasted state

A randomized, double-blind, placebo-controlled study was undertaken in 20 hypertriglyceridemic men [plasma triglyceride (TG), >2.3 mM] with low levels (<0.9 mM) of high-density lipoprotein cholesterol (HDL-C) to investigate the ability of micronized fenofibrate (Tricor or Lipidil; 200 mg/day) to affect atherogenic and thrombogenic plasma risk factors in the fed and fasted state. Each patient underwent (a) 4 weeks of dietary stabilization, (b) 8 weeks of treatment with fenofibrate or placebo, (c) a 5-week washout period, and (d) 8-weeks of treatment with the alternative medication. An oral fat-loading test (1 g fat/kg body weight) was carried out after both treatment periods. Before treatment, patients had a mean (+/- SD) total plasma TG of 3.31+/-0.93 mM; total C, 5.75+/-0.89 mM; HDL-C, 0.71+/-0.09 mM; and low-density lipoprotein (LDL)-C, 3.40+/-0.68 mM. Compared with placebo, fenofibrate reduced fasting TG levels by 36%, and triglyceride-rich lipoprotein (TRL, d<1.006 g/ml) -TG, and TRL-C levels by approximately 40%. In the postprandial state, fenofibrate reduced total TG, TRL-TG, TRL-C, TRL-apoC-III, and TRL-apoE levels by -35% (all values of p<0.01). Fasted and fed HDL-C and apoA-I levels were increased -10%, and total cholesterol/HDL cholesterol ratios were decreased -15% by fenofibrate. No significant differences were observed in mean LDL-C and LDL-apoB levels. A 6% increase in the LDL-C/LDL-apoB ratio during fenofibrate treatment indicated a shift to larger, more buoyant LDL particles. A small, but statistically significant (p<0.01) increase was observed in fasted and fed Lp(a) levels during fenofibrate treatment. Hemostatic parameters were not significantly affected by fenofibrate, except for a 12-15% decrease (p<0.05) in fibrinogen levels in the fasted and fed state, and a significant increase (43%; p<0.05) in fasting levels of plasminogen activator-inhibitor-1. These data demonstrate that micronized fenofibrate is highly effective, in both the fed and fasted state, in reducing TRL lipids and apolipoproteins, and in reducing plasma fibrinogen levels of men with an atherogenic lipoprotein profile.

Fibrates, dyslipoproteinaemia and cardiovascular disease

Recent epidemiological data have reaffirmed that elevated plasma triglyceride and low HDL-cholesterol levels are important risk factors for atherosclerotic vascular disease. The rationale for the clinical use of fibric acid derivatives, which are designed to correct this metabolic nexus, is now on firmer ground. The mechanism of action of fibrates on lipoprotein metabolism has recently been elucidated at the molecular level and involves the activation of peroxisome proliferator-activated receptor-alpha 1 in the liver, with the net effect of improving the plasma transport rates of several lipoproteins. Other potential anti-atherothrombotic effects include the inhibition of coagulation and enhancement of fibrinolysis, as well as the inhibition of inflammatory mediators involved in atherogenesis. These consequences probably underpin the favourable effects of fibrates seen in recent angiographic and clinical trials. Two important clinical trials on the effect of gemfibrozil (Veterans Administration-HDL-Cholesterol Intervention Trial) and bezafibrate (Bezafibrate Infarction Prevention Study) have recently been completed in subjects with elevated triglyceride, low HDL and normal or near-normal LDL-cholesterol levels. The results testify to the efficacy of these agents in decreasing the incidence of cardiovascular events, particularly in patients with multiple risk factors and plasma triglyceride levels of over 2.2 mmol/l. The findings of these trials are compared with the statin-based Air Force/Texas Coronary Atherosclerosis Prevention Study, with a recommendation that future studies in appropriately selected patients should examine the synergistic effect of the fibrate/statin combination. The absolute risk reduction in the incidence of coronary events in the Veterans Administration-HDL-Cholesterol Intervention Trial compares favourably with the statin trials. The therapeutic aspects of the efficacy and safety of fibrates are reviewed. Besides primary mixed hyperlipidaemias, particular indications for the clinical use of fibrates include type 2 diabetes, the metabolic syndrome and renal insufficiency. The St Mary's, Ealing, Northwick Park Diabetes Cardiovascular Disease Prevention Study has suggested that fibrates may decrease the incidence of coronary events in type 2 diabetes, but this hypothesis will be more extensively tested in the Diabetes Atherosclerosis Intervention Study, Fenofibrate in Event Lowering in Diabetes Study and Lipids in Diabetes Study projects. Although significant new knowledge has accrued over the past few years concerning the fundamental and clinical aspects of fibrates, the success of these agents in clinical practice depends on the availability of methods for assessing cardiovascular risk as well as on treatment guidelines, which as presently designed and recommended may be inaccurate and suboptimal.

Peroxisome proliferator-activated receptor-alpha activators regulate genes governing lipoprotein metabolism, vascular inflammation and atherosclerosis

The peroxisome proliferator-activated receptors (PPARs) [alpha, delta (beta) and gamma] form a subfamily of the nuclear receptor gene family. All PPARs are, albeit to different extents, activated by fatty acids and derivatives; PPAR-alpha binds the hypolipidemic fibrates whereas antidiabetic glitazones are ligands for PPAR-gamma. PPAR-alpha activation mediates pleiotropic effects such as stimulation of lipid oxidation, alteration in lipoprotein metabolism and inhibition of vascular inflammation. PPAR-alpha activators increase hepatic uptake and the esterification of free fatty acids by stimulating the fatty acid transport protein and acyl-CoA synthetase expression. In skeletal muscle and heart, PPAR-alpha increases mitochondrial free fatty acid uptake and the resulting free fatty acid oxidation through stimulating the muscle-type carnitine palmitoyltransferase-I. The effect of fibrates on the metabolism of triglyceride-rich lipoproteins is due to a PPAR-alpha dependent stimulation of lipoprotein lipase and an inhibition of apolipoprotein C-III expressions, whereas the increase in plasma HDL cholesterol depends on an overexpression of apolipoprotein A-I and apolipoprotein A-II. PPARs are also expressed in atherosclerotic lesions. PPAR-alpha is present in endothelial and smooth muscle cells, monocytes and monocyte-derived macrophages. It inhibits inducible nitric oxide synthase in macrophages and prevents the IL-1-induced expression of IL-6 and cyclooxygenase-2, as well as thrombin-induced endothelin-1 expression, as a result of a negative transcriptional regulation of the nuclear factor-kappa B and activator protein-1 signalling pathways. PPAR activation also induces apoptosis in human monocyte-derived macrophages most likely through inhibition of nuclear factor-kappa B activity. Therefore, the pleiotropic effects of PPAR-alpha activators on the plasma lipid profile and vascular wall inflammation certainly participate in the inhibition of atherosclerosis development observed in angiographically documented intervention trials with fibrates.