Elsevier

Atherosclerosis

Volume 178, Issue 1, January 2005, Pages 1-7
Atherosclerosis

A potent activator of PPARα and γ reduces the vascular cell recruitment and inhibits the intimal thickning in hypercholesterolemic rabbits

https://doi.org/10.1016/j.atherosclerosis.2004.08.015Get rights and content

Abstract

Peroxisome proliferator-activated receptors (PPARs) regulate the vascular cell functions as well as systemic lipid and glucose metabolism. Here, we studied the effect of TAK-559, a newly developed potent activator both for PPARα and γ, on the vascular cell recruitment. TNF-α - or interleukin-1β (IL-1β)-induced THP-1 cell attachment to cultured endothelial cells was significantly reduced in the presence of 10 μM TAK-559 (P < 0.05). The secretion of monocyte chemoattractant protein-1 (MCP-1) from endothelial cells is reduced by 36% in the presence of 10 μM TAK-559, accompanied with the decreased mRNA expression in the cells. The proliferation and migration of cultured smooth muscle cells (SMCs) were significantly decreased in the presence of TAK-559 (P < 0.05). TAK-559-treated hypercholesterolemic rabbits showed the significant reduction of intimal thickning after balloon catheterization by 51% compared with control (P < 0.05), although the plasma lipid and glucose level was not changed between them. The numbers of macrophage and SMCs were decreased to 34% and 49% in the hyperplastic intima of arteries from TAK-559-treated rabbits compared to those from control, respectively. These results suggest that the PPARα and γ activator inhibits the recruitment of macrophages and SMCs in intima, possibly leading to the reduction of intimal hyperplasia in hypercholesterolemia.

Introduction

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors, and play an important role in the regulation of vascular cell functions as well as of systemic lipid and glucose metabolism, possibly leading to the inhibition of progression of athrosclerosis [1]. One of PPARs, PPARγ, is inclusively expressed in the arterial wall, such as endothelial cells, macrophages, mononuclear cells and smooth muscle cells (SMCs) in atherosclerotic plaques [2], [3]. PPARγ is known to regulate these cellular functions including anti-inflammatory and anti-atherogenic actions, as well as inhibitory effects on proliferation and migration of above vascular cells in atheroma [2], [3], [4], [5]. In fact, we and others have shown that PPARγ activators reduce the intimal hyperplasia after balloon injury in diabetic models [6], as well as the progression of atherosclerosis in diabetic or hypercholesterolemic models [7], [8]. On the other hand, the vascular effects of other activators for PPARs, particularly PPARα, on the vascular cells in vivo remain to be fully elucidated, although the regulatory actions for the macrophages and SMCs have been suggested in vitro [9], [10].

Pioglitazone, a PPARs activator which is world-widely used as an insulin sensitizer for diabetic patients, suppresses carotid intimal thickning accompanied with decreased density of SMCs in intima in diabetic fatty rats [6]. We have shown that the growth and migration activities of SMCs are induced in cultured SMCs isolated from the arteries of diabetic animals compared to normal in vitro [6]. Therefore, the suppression by pioglitazone is largely caused by inhibitory effect on the growth of SMCs, which is resulted from metabolic improvement of diabetes.

TAK-559 is a recently developed, potent activator both for PPARγ and PPARα [11]. The EC50 values for human PPARs activation are 31 nM (γ) and ∼67 nM (α), respectively, which concentrations are 16-fold and more than 150-fold lower than those of pioglitazone [12]. Here, we show the inhibitory effect of TAK-559 on the vascular cell recruitment both in vitro and in vivo. Our study using cultured vascular cells, as well as hypercholesterolemic and non-diabetic model, show that the PPARα and γ activator reduces the intimal hyperplasia in hypercholesterolemia, possibly mediated by the inhibitory effects on the recruitment of macrophages and SMCs, independent of the improvement of serum lipid and glucose levels.

Section snippets

Reagents

Recombinant human TNF-α (hTNF-α), interleukin-1β (IL-1β) and PDGF-BB were purchased from R&D systems (Minneapolis, MN, USA). TAK-559 and pioglitazone were from Takeda Chemical Industries (Osaka, Japan). Rosiglitazone was from GlaxoSmithKline research and Development Limited (Brentford, England). Dulbecco's modified Eagle's medium (DMEM) containing 5.5 mmol/L glucose, Ham's F-12 medium, APMSF and leupeptin were purchased from Sigma Chemical Co. (St. Louis, MS, USA). Fetal bovine serum (FBS) and

Inhibitory effect of TAK-559 on the macrophage recruitment in vitro

In order to know the effect of TAK-559 on macrophage recruitment in vitro, we studied macrophage attachment to endothelial cells, which is known to be important in the process of intimal hyperplasia. As shown in Fig. 1A, TNF-α-induced THP-1 cell attachment to endothelial cells was significantly reduced in the presence of 10 μM TAK-559. As shown in Fig. 1B, the IL-1β-induced THP-1 cell attachment to endothelial cells was also significantly reduced in the presence of 1 and 10 μM TAK-559. There was

Discussion

In this study, we identified the effects of a newly developed dual PPARs agonist, TAK-559, on the vascular cell recruitment in vitro and the intimal thickning by the balloon catheterization using hypercholesterolemic, non-diabetic rabbits. The potent agonist both for PPARα and PPARγ showed the strong inhibition of intimal hyperplasia, although the plasma lipids, glucose and insulin levels were not changed min the rabbits. The inhibitory effect was thought to be caused by the strong inhibition

Acknowledgements

These studies were supported by grants from the Japanese Ministry of Education, Culture, Sports, Science and Technology to Y.S. and H.B. We thank Drs. M. Igarashi (Yamagata Univ.) and A. Haruno (Taiho Pharmacological Co.) for the instruction of balloon catheterization method. The authors are grateful to Takeda Chemical Industries, Ltd. for the supply of TAK-559 and pioglitazone, and for valuable suggestions. The authors are also grateful to GlaxoSmithKline for the supply of Rosiglitazone.

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