Paradoxical effects of polyphenolic compounds from Clusiaceae on angiogenesis

Abstract

Clusiaceae plants display high contents of xanthones and coumarins, the effects of which on endothelium, more particularly on angiogenesis, have not been assessed yet. We screened the capacity of six molecules from Clusiaceae – belonging to xanthones, coumarins and acid chromanes classes – to induce endothelium-dependent relaxation on mice aortic rings. Endothelial nitric oxide (NO) production was assessed in endothelial cell line using electron paramagnetic resonance technique. Then, the capacity of these molecules to induce capillary-like structures of endothelial cells was assessed. Cellular processes implicated in angiogenesis (adhesion, migration and proliferation) and Western blot analyses were then investigated. Among the tested molecules, isocalolongic acid (IA) and 2-deprenylrheediaxanthone (DRX) induced an endothelium-dependent relaxation of the aorta associated with an increase of NO production in endothelial cells. Using in vitro and ex vivo angiogenesis assays, it was shown that IA treatment promoted the formation of capillary-like network. In contrast, DRX prevented the ability of vascular endothelial growth factor (VEGF) to increase the formation of capillary-like network. IA increased endothelial cell proliferation while DRX decreased all cellular processes of angiogenesis. Western blot analysis showed that IA increased VEGF expression whereas DRX decreased ICAM-1 expression. Altogether, these data allowed identifying isolated molecules from Clusiaceae that exhibit a potential activity towards the modulation of endothelium-dependent relaxation involving NO release. Interestingly, they also highlighted paradoxical effects of the two compounds on cellular angiogenic processes, IA being pro-angiogenic and DRX anti-angiogenic.

Introduction

Natural dietary polyphenolic compounds present in a wide variety of plants are thought to protect against cardiovascular disease and cancer [1], [2]. Polyphenols are a large family of natural compounds widely distributed in plants that include flavonoids and non-flavonoids. Flavonoids are the most studied polyphenols on cardiovascular system. Among non-flavonoids, xanthones, coumarins and acid chromanes are less investigated. Family Clusiaceae is known to biosynthesize the above polyphenolic compounds [3] and Clusiaceous species are widely distributed in tropical Asia, Africa, New Caledonia and Polynesia [4]. In the past few years, a large number of xanthones and coumarins have been identified from these species and they exhibit various biological activities such as antifungal, antimalarial, cytotoxic and antioxidant properties [5], [6], [7], [8].

One of the therapeutic relevant effects of polyphenols on the cardiovascular system may be their ability to interact with the nitric oxide (NO)-generating pathway in vascular endothelium [9]. Xanthones and coumarins can act on the endothelium either by increasing NO release [10], [11] or decreasing level of NO synthase inhibitors [12]. However, little information has been reported on biological activities of acid chromanes on endothelium.

Angiogenesis is a complex process characterized by the early degradation of extracellular matrix, essentially by matrix metalloproteinases, followed by migration and proliferation of endothelial cells and the maturation of the new blood vessel in response to local pro-angiogenic factors such as vascular endothelial growth factor (VEGF) [13].

The present study was designed to screen the effect of unrecognized polyphenolic compounds isolated from plants belonging to family Clusiaceae on the endothelium (Fig. 1). More precisely, we screened the capacity of six molecules belonging to xanthones, acid chromanes and coumarins classes to induce endothelium-dependent relaxation on isolated blood vessels and NO release from endothelial cells. Since NO can act on the expression of protective genes of the cardiovascular system, including the regulation of angiogenesis, the molecules able to induce endothelium-dependent vasodilatation were then assessed on the different cellular processes implicated on angiogenesis: cell migration, proliferation, adhesion and the formation of capillary-like structures.