A New Isoxazolic Compound Acts as α7 Nicotinic Receptor Agonist in Human Umbilical Vein Endothelial Cells

Recent evidence suggests that the α7 nicotinic acetylcholine receptors (α7 nAChRs) participate in the development of angiogenesis and could be a new endothelial target for revascularization in therapeutic angiogenesis. It has been shown that in human umbilical vein endothelial cells (HUVECs) α7 nAChR agonists increase the intracellular calcium concentration ([Ca²⁺]_i), thus inducing proliferation and vessel formation which are important stages of angiogenesis. In the present study we evaluated the effect of new isoxazole compounds on the cytosolic Ca²⁺ signal in HUVECs using the fluorescent Ca²⁺ indicator Fluo-3AM and probing the involvement of α7 nAChR by means of pharmacological tools. HUVECs expressed mainly α7 nAChR, since there was no significant difference in the increase in [Ca²⁺]_i induced by nicotine, a non-selective nicotinic agonist, in relation to choline, a selective α7 nAChR agonist. The increase in [Ca²⁺]_i induced by 1 mM choline was inhibited significantly (p = 0.014) in cells which had been pre-incubated for 15 min with methyllycaconitine (MLA), a selective α7 nAChR antagonist. The studied compounds 1, 2, and 3 induced an increase in [Ca²⁺]_i in a dose-dependent manner. Compound 1 at 10 mM induced a greater increase in [Ca²⁺]_i than compounds 2 and 3. The increase in [Ca²⁺]_i induced by compound 1 was significantly inhibited by MLA (p = 0.013) and completely inhibited by mecamylamine, a non-selective nAChR antagonist, indicating that the isoxazolic compound 1 acts as an α7 nAChR agonist.