Abstract 541: Adenosine Inhibits C-Kit+ Progenitor Smooth Muscle Cell (P-SMC) Infiltration In Injury-Induced Neointima Formation And Human P-SMC Growth: Role of A2B Adenosine Receptor-Mediated Growth Regulation

Abstract

Adenosine inhibits injury-induced neointimal formation; however, the mechanism is incompletely understood. Marrow-derived C-Kit+ progenitor cells (P-SMCs) express a smooth muscle phenotype and contribute to injury-induced neointimal thickening. The goal of our investigation was to determine whether adenosine attenuates neointimal hyperplasia in part by inhibiting the growth of P-SMCs and to clarify which adenosine receptor subtypes are involved. Digitized pixel analysis demonstrated that administration of adenosine (20 μM) peri-arterially for 7 days in a slow-release formulation inhibited injury-induced neointimal hyperplasia in the rat carotid artery by 71% (p<0.05: neointimal thickness: 37,424 ± 18,371 pixels in vehicle-treated [n=7] versus 10,352 ± 2,824 pixels in adenosine-treated [n=7]). Microscopic analysis following immunostaining for c-Kit+ cells showed a marked decrease (> 50%) in staining for c-Kit+ cells in the neointima of rats receiving adenosine. In cultured human P-SMCs, serum-induced growth (as determined by quantification of DNA synthesis and cell number), cell-migration, and collagen synthesis was inhibited by adenosine and 2-chloroadenosine, but not by N 6 -cyclopentyladenosine (selective A 1 -receptor agonist), CGS21680 (selective A 2A -receptor agonist) or N 6 -(3-iodobenzyl)adenosine-5'-N-methyluronamide (selective A 3 -receptor agonist). This agonist profile was consistent with an A 2B -receptor-mediated effect. Augmentation of endogenous adenosine levels with erythro -9-(2-hydroxy-3-nonyl)adenine (adenosine deaminase inhibitor) and 5-iodotubericidin (adenosine kinase inhibitor) attenuated P-SMC growth. Moreover the antimitogenic effects of both exogenous and endogenous adenosine were abrogated by blockade of A 2B receptors (MRS 1754), but not by antagonism of A 1 (8-cyclopentyl-1,3-dipropylxanthine), A 2A (SCH 58261) or A 3 (VUF 5574) receptors. We conclude that adenosine, via activation of A 2B receptors, inhibits neointimal formation in part by inhibiting infiltration and growth of C-Kit+ P-SMCs. These findings suggest that A 2B receptor stimulation may prevent vascular remodeling associated with coronary artery disease, hypertension, atherosclerosis and restenosis.