The angiotensin receptor blocker, azilsartan medoxomil (TAK-491), suppresses vascular wall expression of plasminogen activator inhibitor type-I protein potentially facilitating the stabilization of atherosclerotic plaques

Increased expression of plasminogen activator inhibitor type-I (PAI-1) in vessel walls seems to accelerate atherosclerosis. Angiotensin II can increase the synthesis of PAI-1. Inhibition of this process may facilitate migration of vascular smooth muscle cells (VSMCs) stabilizing atherosclerotic plaques. To determine whether the inhibition of the angiotensin II type 1 receptor can blunt the expression of PAI-1 protein in the aortic wall, we administered azilsartan medoxomil (AZL-M), a prodrug of an angiotensin II type 1 receptor blocker developed by the Takeda Pharmaceutical Company Limited, for 16 weeks to ApoE knockout mice on a high fat diet rendered overexpressors of PAI-1 in VSMCs. Homogenates of the pooled aortas from each group were assayed for PAI-1 by enzyme-linked immunosorbent assay. Cellularity of atherosclerotic lesions was assessed by 4',6-diamidino-2-phenylindole staining in sections of aortic lesions, and collagen content in the lesions was quantified by immunohistochemistry. Aortic wall PAI-1 was decreased by each of the 3 dosage regimens of AZL-M (0.1-10 mg/kg). Cellularity and collagen were increased in lesions from mice given AZL-M, consistent with the development of more stable plaques. Accordingly, the suppression of PAI-1 expression by AZL-M may attenuate the evolution of atherosclerotic plaques vulnerable to rupture.     

PPAR agonists in the treatment of atherosclerosis

Current treatment for atherosclerotic heart disease consists mainly of the administration of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors or 'statin' class of drugs. Statins, which lower low-density lipoprotein cholesterol levels and have numerous other effects in the arterial wall, have shown remarkable efficacy and an exemplary safety profile in preventing both primary and secondary atherosclerotic events. These agents, however, are less effective at raising high-density lipoprotein, lowering triglycerides and decreasing insulin resistance--all of which are important targets for the prevention of ischemic vascular disease. Agonists of the peroxisome proliferator-activated receptors (PPARs) are among the most promising drug candidates to target these treatment gaps. Only PPARalpha agonists have been shown clinically to improve the outcome of atherosclerotic heart disease; however, it will only be a matter of time before we know whether compounds that modulate the function of PPARgamma and beta/delta are also efficacious at combating atherosclerosis.     

Pleiotropic vascular effects of PPARgamma ligands

Peroxisome proliferator-activated receptor-gamma (PPARgamma) ligands have been used for several years as modulators of insulin sensitivity and glucose metabolism. Recent data from numerous studies have shown that PPARgamma ligands have numerous beneficial effects in the vasculature. They have been shown to regulate proliferation and migration of vascular smooth muscle cells as well as improving endothelial cell function. They improve blood pressure by actions at the resistance arteries and kidneys. Clinical trials have indicated that PPARgamma ligands can minimize the development of atherosclerosis as well as regulating other vascular inflammation. PPARgamma has been detected in all the cells found in the vessel wall as well as those cells associated with vascular pathophysiologies. In the monocyte/macrophage, PPARgamma ligands downregulate production of inflammatory cytokines and migration. Also, PPARgamma ligands regulate the expression of SR-A and CD36 receptors that take up lipids in the macrophage. PPARgamma has also been demonstrated to act through the liver X receptor alpha to increase the activity of reverse cholesterol transport in these cells. In dendritic cells and T-cells, PPARgamma ligands have been shown to inhibit activation and the initiation of inflammation. Inflammatory cytokines are downregulated in animal models administered PPARgamma ligands, leading to decreased atherosclerosis. While PPARgamma ligands have been useful in the treatment of type 2 diabetes, the important vasculoprotection elicited by these compounds could prove to be of greater benefit in the future.     

Nanomedicine for the prevention,treatment and imaging of atherosclerosis

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in developed countries, with an increasing prevalence due to an aging population. The pathology underpinning CVD is atherosclerosis, a chronic inflammatory state involving the arterial wall. Accumulation of low density lipoprotein (LDL) laden macrophages in the arterial wall and their subsequent transformation into foam cells lead to atherosclerotic plaque formation. Progression of atherosclerotic lesions may gradually lead to plaque related complications and clinically manifest as acute vascular syndromes including acute myocardial or cerebral ischemia. Nanotechnology offers emerging therapeutic strategies, which may have advantage overclassical treatments for atherosclerosis. In this review, we present the potential applications of nanotechnology toward prevention, identification and treatment of atherosclerosis.     

NPY and NPY receptors in vascular remodeling

Neuropeptide Y (NPY) is a sympathetic neurotransmitter that acts on multiple receptors (Y1-Y6) and exerts a variety of cardiovascular effects. Originally known as a vasoconstrictor acting on Y1 receptors, NPY is also a potent angiogenic factor as well as a powerful stimulator of vascular smooth muscle proliferation and atherogenesis in vitro and in vivo. These two types of vascular remodeling are predominantly mediated by Y2/Y5 and Y1 receptors respectively, but evidence suggests that all receptors are activated in both conditions. A strategy to inhibit neointima formation and atherosclerotic lesions without impairing ischemic angiogenesis and collateral vessel formation has been a major challenge to overcome. Studies in rodents show that Y1 receptor antagonist inhibits angioplasty-induced atherosclerotic-like vascular remodeling, without affecting ischemic revascularization. Conversely, Y2 receptor activation appears to be sufficient to stimulate angiogenesis in various animal models. Thus, the use of selective receptor agonists to promote angiogenesis through the Y2 receptor while antagonizing the pro-atherosclerotic and pro-stenotic effects with Y1 receptor-selective antagonists may help to successfully treat vascular remodeling in cardiovascular diseases.     

Therapeutic potential and strategies against leukocyte-platelet interaction in atherosclerosis

Leukocyte rolling, adhesion, transmigration and activation are features of vascular inflammation leading to atherosclerosis. In particular the interaction between platelets and leukocytes is a key process for adhesion of inflammatory cells to the vascular wall. The various mechanisms of the specific platelet-leukocyte interaction may provide a powerful target to prevent initiation and/or progression of atherosclerotic lesions.     

The Role of PPARgamma Ligands as Regulators of the Immune Response

A major challenge in medical research is to break the traditional compartmentalization that frequently separates different fields. Unexpected linkages between different areas of medicine are often of particular interest. An unsuspected "bridge" across clinical cardiology and basic immunology, as presented in this review, is a good example of such a linkage. Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a role in glucose homeostasis and adipocyte differentiation and has been implicated in diabetes mellitus, a metabolic disorder predisposing to atherosclerosis. In addition, PPARgamma ligands of the antidiabetic thiazolidinediones group exert beneficial effects on atherosclerosis. Expression of major histocompatibility complex class II (MHC class II), a key molecule in the immune response, has recently been observed in atherosclerotic plaques. In recent years, important effects of PPARgamma ligands on MHC class II expression, activated T lymphocytes and macrophage activation have been described. Using atherosclerosis as a model of an immune-mediated disease, we summarize in this review the recent exciting observations that link PPARgamma to the immune response. (c) 2002 Prous Science. All rights reserved.     

Synergistic vascular protective effects of combined low doses of PPARalpha and PPARgamma activators in angiotensin II-induced hypertension in rats

BACKGROUND AND PURPOSE: Protective cardiovascular effects of peroxisome proliferator activated receptor (PPAR)alpha and PPARgamma activators have been demonstrated. If used as vasoprotective agents in high risk vascular patients rather than for their metabolic benefits, these agents could be associated with unwanted side effects. As a proof of concept to support the use of combined low doses of PPARalpha and PPARgamma as vascular protective agents in high risk vascular patients, we tested the hypothesis that combined low doses of PPARalpha (fenofibrate) and PPARgamma (rosiglitazone) activators would provide vascular protective benefits similar to full individual doses of these PPAR agonists. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats infused with Ang II (120 ng kg(-1) min(-1)) were treated with rosiglitazone (1 or 2 mg kg(-1) day(-1)) alone or concomitantly with fenofibrate (30 mg kg(-1) day(-1)) for 7 days. Thereafter, vessels was assessed on a pressurized myograph, while NAD(P)H oxidase activity was determined by lucigenin chemiluminescence. Inflammation was evaluated using ELISA for NFkappaB and Western blotting for adhesion molecules. KEY RESULTS: Ang II-induced blood pressure increase, impaired acetylcholine-induced vasorelaxation, altered vascular structure, and enhanced vascular NAD(P)H oxidase activity and inflammation were significantly reduced by low dose rosiglitazone+fenofibrate. CONCLUSIONS AND IMPLICATIONS: Combined low doses of PPARalpha and PPARgamma activators attenuated development of hypertension, corrected vascular structural abnormalities, improved endothelial function, oxidative stress, and vascular inflammation. These agents used in low-dose combination have synergistic vascular protective effects. The clinical effects of combined low-dose PPARalpha and PPARgamma activators as vascular protective therapy, potentially with reduced side-effects and drug interactions, should be assessed.     

Prostaglandin J2 family and the cardiovascular system

Prostaglandins (PGs) of the J2 family including PGJ2, delta12-PGJ2, and 15-deoxy-delta12,14-PGJ2 (15d-PGJ2) are naturally occurring metabolites of PGD2. Among them, 15d-PGJ2 is a powerful ligand for the peroxisome proliferator-activated receptor-gamma (PPARgamma). 15d-PGJ2 and synthetic PPARgamma ligands have been reported to exert several effects on vascular cells, such as anti-proliferative, differentiation-inducing, anti-apoptotic, and anti-inflammatory effects, most of which seem to be atheroprotective, although PPARgamma-independent mechanisms may be involved. Vascular endothelial cells, intimal smooth muscle cells, and cardiomyocytes express lipocalin-type PGD synthase (L-PGDS) in vivo, which catalyzes the isomeric conversion of PGH2 to PGD2. L-PGDS expression in endothelial cells is stimulated by laminar fluid shear stress. PGD2 and 15d-PGJ2 are detected in the culture medium of endothelial cells exposed to shear stress. Serum and urinary levels of L-PGDS increase in diseases with vascular injuries, such as hypertension and diabetes. Based on these findings, we hypothesize that PGs of the J2 series are physiological substances produced in the vascular wall to protect vascular cells from injurious stimuli and to repress inflammatory reactions. If this hypothesis is correct, PGJ2 family members or other similar substances may provide novel preventive and therapeutic strategies for the treatment of vascular diseases.     

Rosiglitazone, a PPARgamma ligand, modulates signal transduction pathways during the development of acute TNBS-induced colitis in rats

Recent studies have shown that peroxisome proliferator-activated receptor gamma (PPARgamma), a highly nuclear receptor expressed in the colon, may participate in the control of inflammation, especially in regulating the production of immunomodulatory and inflammatory mediators, cellular proliferation and apoptosis. In order to delve into the anti-inflammatory mechanisms and signalling pathways of PPARgamma agonists, we have studied the effects of rosiglitazone, a PPARgamma agonist on the extent and severity of acute ulcerative colitis caused by intracolonic administration of 2,4,6-trinitribenzene sulfonic acid (TNBS) in rats. The inflammatory response was assessed by gross appearance, myeloperoxidase (MPO) activity, tumour necrosis factor alpha (TNF-alpha) levels and a histological study of the lesions. We determined prostaglandin E2 production as well as the cyclooxygenases (COX)-1 and -2 expressions by immunohistochemistry and Western blotting. The nuclear factor kappa (NF-kappaB) p65 and p38 mitogen-activated protein kinase (MAPK) expression levels were also measured by Western blotting. Finally, since PPARgamma agonists modulate apoptosis, we tried to clarify its effects under early acute inflammatory conditions. Inflammation following TNBS induction was characterized by increased colonic wall thickness, edema, diffuse inflammatory cells infiltration, necrosis reaching an ulcer index (UI) of 9.66+/-0.66 cm(2) and increased MPO activity and TNF-alpha colonic levels. Rosiglitazone treatment significantly reduced the morphological alteration associated with TNBS administration and the UI with the highest dose. In addition, the degree of neutrophil infiltration and the cytokine levels were significantly ameliorated. Rosiglitazone significantly reduced the rise in the prostaglandin (PG) E(2) generation compared with TNBS group. The COX-1 levels remained stable throughout the treatment in all groups. The COX-2 expression was elevated in TNBS group; however rosiglitazone administration reduced the COX-2 overexpression. A high expression of NF-kappaB p65 and p38 MAPK proteins appeared in colon mucosa from control TNBS-treated rats; nevertheless, PPARgamma agonist treatment drastically decreased them. There were no significant changes in apoptosis after rosiglitazone treatment when compared to TNBS group. In conclusion, rosiglitazone seems to modulate the acute colitis through NF-kappaB p65 and p38 MAPK signalling pathways.     

Peroxisome proliferator-activated receptors in the cardiovascular system

Peroxisome proliferator-activated receptor (PPAR)s are a family of three nuclear hormone receptors, PPARalpha, -delta, and -gamma, which are members of the steriod receptor superfamily. The first member of the family (PPARalpha) was originally discovered as the mediator by which a number of xenobiotic drugs cause peroxisome proliferation in the liver. Defined functions for all these receptors, until recently, mainly concerned their ability to regulate energy balance, with PPARalpha being involved in beta-oxidation pathways, and PPARgamma in the differentiation of adipocytes. Little is known about the functions of PPARdelta, though it is the most ubiquitously expressed. Since their discovery, PPARs have been shown to be expressed in monocytes/macrophages, the heart, vascular smooth muscle cells, endothelial cells, and in atherosclerotic lesions. Furthermore, PPARs can be activated by a vast number of compounds including synthetic drugs, of the clofibrate, and anti-diabetic thiazoldinedione classes, polyunsaturated fatty acids, and a number of eicosanoids, including prostaglandins, lipoxygenase products, and oxidized low density lipoprotein. This review will aim to introduce the field of PPAR nuclear hormone receptors, and discuss the discovery and actions of PPARs in the cardiovascular system, as well as the source of potential ligands.     

High‐density lipoproteins,platelets and the pathogenesis of atherosclerosis

1. Prospective and interventional studies demonstrate an inverse relationship between plasma high‐density lipoprotein (HDL)–cholesterol and the incidence of coronary artery disease. Although the atheroprotective effects of HDL are usually attributed to the reverse cholesterol transport, in which HDL shuttles cholesterol from cells in the arterial wall to the liver, other mechanisms are also under investigation. 2. Platelets are involved in both the initiation and progression of atherosclerotic lesions. In addition, the formation of thrombi over ruptured atherosclerotic plaques results in the narrowing or complete occlusion of coronary arteries. Current experimental evidence suggests that HDL may exert antiplatelet effects and thereby counteract the development of atherothrombotic vascular disease. 3. In vitro studies show that HDL inhibits agonist‐stimulated platelet aggregation, fibrinogen binding, granule secretion and liberation of thromboxane A₂. Inhibitory effects of HDL are mediated, in part, by scavenger receptor type B1 and/or the apolipoprotein E receptor apoER2/LRP8 and are linked to the induction of intracellular signalling cascades encompassing stimulation of protein kinase C, cytoplasmatic alkalization and generation of nitric oxide. 4. Populational studies demonstrate that there is an inverse association between plasma HDL levels and recurrent venous thromboembolism. In addition, HDL–cholesterol has been identified as an independent predictor of acute platelet thrombus formation. The administration of reconstituted HDL particles in humans attenuates ex vivo platelet activation. 5. The present review summarizes recent advances in understanding HDL–platelet interactions and discusses the potential use of HDL‐like particles in the therapy of thrombosis.     

Vascular benefits of angiotensin receptor blockers

There is convincing evidence that angiotensin II, through activation of the angiotensin II type 1 (AT1) receptor, is involved in the atherosclerotic process. Similarly, angiotensin receptor blockers decrease vascular inflammation, hypertrophy and thrombosis, which are the key components of the progression of atherosclerosis. In addition, in several animal models, angiotensin receptor blockade was able to inhibit atherosclerosis. However, the effects of angiotensin receptor blockers on clinical outcome in cardiovascular patients remains to be established. Contradictory results have been found on the reduction of the risk on myocardial infarctions and in-stent restenosis, although there is solid evidence for cerebroprotective effects of these receptor blockers. These differences may be related to the role of the AT2 receptor. This review discusses the role of angiotensin II and angiotensin receptor blockers in the atherosclerotic process and its translation into clinical practice.     

Vascular benefits of angiotensin receptor blockers

There is convincing evidence that angiotensin II, through activation of the angiotensin II type 1 (AT1) receptor, is involved in the atherosclerotic process. Similarly, angiotensin receptor blockers decrease vascular inflammation, hypertrophy and thrombosis, which are the key components of the progression of atherosclerosis. In addition, in several animal models, angiotensin receptor blockade was able to inhibit atherosclerosis. However, the effects of angiotensin receptor blockers on clinical outcome in cardiovascular patients remains to be established. Contradictory results have been found on the reduction of the risk on myocardial infarctions and in-stent restenosis, although there is solid evidence for cerebroprotective effects of these receptor blockers. These differences may be related to the role of the AT2 receptor. This review discusses the role of angiotensin II and angiotensin receptor blockers in the atherosclerotic process and its translation into clinical practice.