Platelet‐mediated angiogenesis is independent of VEGF and fully inhibited by aspirin

Abstract

Background and Purpose Platelets are major players in every step of vessel development through the local delivery of angiogenesis‐modulating factors, including the pro‐angiogenic protein VEGF and the anti‐angiogenic endostatin. Although thrombin is a potent agonist and is highly elevated in angiogenesis‐related diseases, studies regarding its action on the release of platelet angiogenic factors are scarce and controversial. Herein, we have investigated the role of thrombin not only in VEGF and endostatin release but also in net platelet angiogenic activity. Experimental Approach Human platelets were stimulated with thrombin in the presence of the various inhibitors of the signalling pathways involved in platelet activation. Supernatants/releasates were used to determine the levels of angiogenic molecules and to induce angiogenic responses. Key Results We found that thrombin induced the secretion of both VEGF and endostatin; however, the overall effect of the releasates was pro‐angiogenic as they promoted tubule‐like formation and increased the proliferation of endothelial cells. Both responses were only slightly suppressed in the presence of a VEGF receptor‐neutralizing antibody. Pharmacological studies revealed that while inhibitors of PKC, p38, ERK1/2, Src kinases or PI3K/Akt exerted only partial inhibitory effects, aspirin fully blocked the pro‐angiogenic activity of the releasate. Conclusions and Implications In contrast to current belief, platelet pro‐angiogenic responses are independent of VEGF and appear to be the result of the combined action of several molecules. Moreover, our data reinforce the notion that aspirin is a good candidate for a therapeutic agent to treat angiogenesis‐related diseases.

Stimulation of PAR-1 or PAR-4 promotes similar pattern of VEGF and endostatin release and pro-angiogenic responses mediated by human platelets

“…This study followed principles in the Declaration of Helsinki and received the approval of the Institutional Ethics Committee and written consent from all the subjects. WPs (4 Â 10 8 /ml) and PRP were obtained as previously described [11] and then stimulated with human alpha-thrombin (Enzyme Research Laboratories, South Bend, IN), PAR-1-AP (TFLLR-NH 2 ) or PAR-4-AP (AYPGKF-NH 2 ) (Genbiotech SRL, Buenos Aires, Argentina). Platelet's releasates were obtained by centrifugation of the stimulated platelets in the presence of Prostaglandin I 2 (PGI 2 , 75 ng/ml) (Cayman, Ann Arbor, MI) and resting WPs were lysed as previously described [12].…”

“…Human microvascular endothelial cells (HMEC-1) (ATCC Cell Lines) and human late outgrowth endothelial progenitor cells (EPC) were grown as previously described [11,13]. Growth factor medium was replaced by supernatants of PAR-stimulated platelets and endothelial responses were assessed after 18 h. To evaluate the effect of plasma on cell growth and tubule formation, PRP (4 Â 10 8 platelets/ml) was stimulated with PAR-1-AP or PAR-4-AP during 5 min, then centrifuged in the presence of PGI 2 and the calcium level was restored in the citrated plasma by the addition of CaCl 2 (22 mM).…”

“…Previous evidences indicated that these angiogenic regulators are packed into morphologically distinct populations of platelet alpha-granules [3][4][5] and that both molecules can be differentially released upon platelet activation induced by the selective activation of protease-activated receptor (PAR)-1 or PAR-4 [3,4,6] providing a mechanism by which platelets could differentially modulate angiogenesis. Controversially, other studies provided evidences against this hypothesis [5,[7][8][9][10][11], suggesting that the release of VEGF and endostatin mediated by PAR-activation appears to be a stochastic but not a selective process that is regulated by the type and concentration of platelet agonist as well as the duration of platelet activation. We exhaustively characterized the VEGF and endostatin release from platelets activated with PAR-1-activating peptide (AP) and PAR-4-AP by comparing the same variables used in the controversial previous studies, including agonist concentrations, time of stimulation, washed platelets (WPs) or platelet-rich plasma (PRP) and the angiogenic activity of the PARs-stimulated platelet releasates.…”

Aspirin Inhibits Platelet-Derived Sphingosine-1-Phosphate Induced Endothelial Cell Migration

“…Aspirin has been described as a strong inhibitor of platelet pro-angiogenic activity [12]. Borthwick et.…”

Hubungan Beberapa Faktor Klinis dan Pengobatan Penyakit Arteri Koroner dengan Pembentukan dan Gradasi Kolateral Arteri Koroner

“…Pada umumnya obat-obatan kardiovaskular mampu menghambat proses angiogenesis itu melalui berbagai mekanisme. 10 Namun, penelitian lain yang dilakukan Schinkel dkk. 9 menunjukkan sebaliknya, yaitu terdapat suatu peningkatan proliferasi sel otot polos pembuluh darah (suatu penanda aktivitas angiogenesis) pada sediaan dinding aorta manusia yang mendapatkan aspirin.…”