Antiplatelet Actions of Statins and Fibrates Are Mediated by PPARs

Pleiotropic effects of statins. - Basic research and clinical perspectives -

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, which are widely used to lower serum cholesterol levels in the primary and secondary prevention of cardiovascular disease. Recent experimental and clinical evidence suggests that the beneficial effects of statins may extend beyond their cholesterol-lowering effects, to include so-called pleiotropic effects. These cholesterol-independent effects include improving endothelial function, attenuating vascular and myocardial remodeling, inhibiting vascular inflammation and oxidation, and stabilizing atherosclerotic plaques. The mechanism underlying some of these pleiotropic effects is the inhibition of isoprenoid synthesis by statins, which leads to the inhibition of intracellular signaling molecules Rho, Rac and Cdc42. In particular, inhibition of Rho and one of its downstream targets, Rho kinase, may be a predominant mechanism contributing to the pleiotropic effects of statins. The aim of the present review is to provide an update on the non-cholesterol-dependent statin effects in the cardiovascular system and highlight some of the recent findings from bench to bedside to support the concept of statin pleiotropy.

The PPARbeta/delta agonist GW0742 relaxes pulmonary vessels and limits right heart hypertrophy in rats with hypoxia-induced pulmonary hypertension

Background

Pulmonary vascular diseases are increasingly recognised as important clinical conditions. Pulmonary hypertension associated with a range of aetiologies is difficult to treat and associated with progressive morbidity and mortality. Current therapies for pulmonary hypertension include phosphodiesterase type 5 inhibitors, endothelin receptor antagonists, or prostacyclin mimetics. However, none of these provide a cure and the clinical benefits of these drugs individually decline over time. There is, therefore, an urgent need to identify new treatment strategies for pulmonary hypertension.

Methodology/Principal Findings

Here we show that the PPARβ/δ agonist GW0742 induces vasorelaxation in systemic and pulmonary vessels. Using tissue from genetically modified mice, we show that the dilator effects of GW0742 are independent of the target receptor PPARβ/δ or cell surface prostacyclin (IP) receptors. In aortic tissue, vascular relaxant effects of GW0742 were not associated with increases in cGMP, cAMP or hyperpolarisation, but were attributed to inhibition of RhoA activity. In a rat model of hypoxia-induced pulmonary hypertension, daily oral dosing of animals with GW0742 (30 mg/kg) for 3 weeks significantly reduced the associated right heart hypertrophy and right ventricular systolic pressure. GW0742 had no effect on vascular remodelling induced by hypoxia in this model.

Conclusions/Significance

These observations are the first to show a therapeutic benefit of ‘PPARβ/δ’ agonists in experimental pulmonary arterial hypertension and provide pre-clinical evidence to favour clinical trials in man.

Non-genomic effects of PPARgamma ligands: inhibition of GPVI-stimulated platelet activation

BACKGROUND

Peroxisome proliferator-activated receptor-(gamma) (PPAR(gamma)) is expressed in human platelets although in the absence of genomic regulation in these cells, its functions are unclear.

OBJECTIVE

In the present study, we aimed to demonstrate the ability of PPAR(gamma) ligands to modulate collagen-stimulated platelet function and suppress activation of the glycoprotein VI (GPVI) signaling pathway.

METHODS

Washed platelets were stimulated with PPAR(gamma) ligands in the presence and absence of PPAR(gamma) antagonist GW9662 and collagen-induced aggregation was measured using optical aggregometry. Calcium levels were measured by spectrofluorimetry in Fura-2AM-loaded platelets and tyrosine phosphorylation levels of receptor-proximal components of the GPVI signaling pathway were measured using immunoblot analysis. The role of PPAR(gamma) agonists in thrombus formation was assessed using an in vitro model of thrombus formation under arterial flow conditions.

RESULTS

PPAR(gamma) ligands inhibited collagen-stimulated platelet aggregation that was accompanied by a reduction in intracellular calcium mobilization and P-selectin exposure. PPAR(gamma) ligands inhibited thrombus formation under arterial flow conditions. The incorporation of GW9662 reversed the inhibitory actions of PPAR(gamma) agonists, implicating PPAR(gamma) in the effects observed. Furthermore, PPAR(gamma) ligands were found to inhibit tyrosine phosphorylation levels of multiple components of the GPVI signaling pathway. PPAR(gamma) was found to associate with Syk and LAT after platelet activation. This association was prevented by PPAR(gamma) agonists, indicating a potential mechanism for PPAR(gamma) function in collagen-stimulated platelet activation.

CONCLUSIONS

PPAR(gamma) agonists inhibit the activation of collagen-stimulation of platelet function through modulation of early GPVI signalling.

Fenofibrate, simvastatin and their combination in the management of dyslipidaemia in type 2 diabetic patients

OBJECTIVE

To evaluate the efficacy of fenofibrate, simvastatin or their combination in type 2 diabetic patients with combined dyslipidaemia.

RESEARCH DESIGN AND METHODS

241 patients, who had never previously taken lipid-lowering medications, received fenofibrate 145 mg/day, or simvastatin 40 mg/day, or fenofibrate 145 mg/day + simvastatin 40 mg/day combination for 12 months. We evaluated lipids, glycaemic, haemostatic, and inflammatory variables at baseline, and after 6 and 12 months.

RESULTS

After 12 months total cholesterol (TC), LDL cholesterol (LDL-C) and triglycerides (Tg) decreased while HDL cholesterol (HDL-C) increased in all groups, even if the values obtained with fenofibrate + simvastatin were the best. At the end of the study apolipoprotein A-1 (Apo A-1) increased with fenofibrate + simvastatin, while apolipoprotein B (Apo B) decreased in all groups compared to baseline. Plasminogen activator inhibitor-1 (PAI-1) and high-sensitivity C reactive protein (hs-CRP) decreased after 12 months compared to baseline with simvastatin, and with fenofibrate + simvastatin even if the value obtained with fenofibrate-simvastatin was the lowest. After 12 months, fibrinogen (Fg) decreased compared to baseline with fenofibrate + simvastatin.

LIMITATIONS

This study has some limitations. The first one is the relatively small sample of studied patients. The second one is the lack of an advanced lipid proteins evaluation, such as lipoprotein subfraction changes in the different treatment regimen. Finally, we have not selected patients that could show the best response to fibrate (i.e.: hypertriglyceridemics) or statins (i.e.: hypercholesterolemics) monotherapy, so the effect of these drugs administered alone may have been partly attenuated.

CONCLUSIONS

Fenofibrate + simvastatin association improved lipid parameters, prothrombotic and inflammatory factors, and appeared to have a good tolerability profile over 12 months of therapy.