The angiotensin AT2-receptor agonist compound 21 is an antagonist for the thromboxane TP-receptor – Implications for preclinical studies and future clinical use

• Published in: Peptides (New York, N.Y. : 1980) Vol. 164; p. 170990
• Main Authors: Fredgart, Maise H., Leurgans, Thomas M., Stenelo, Martin, Nybo, Mads, Bloksgaard, Maria, Lindblad, Lena, De Mey, Jo G.R., Steckelings, U. Muscha
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.06.2023
• Subjects: Angiotensin AT2-receptors; Beta-arrestin recruitment; Compound 21; Myography; Platelet aggregation; TP-receptors; Myography; NO; Angiotensin AT2-receptors; eNOS; C21; Compound 21; U46619; PD123319; AT1R; Platelet aggregation; AT2R; Ang II; AUC; ARB; PE; ACEI; TP-receptors; TP; β-Gal; Beta-arrestin recruitment
• ISSN: 0196-9781; 1873-5169
• DOI: 10.1016/j.peptides.2023.170990

Since the AT2-receptor (AT2R) agonist C21 has structural similarity to the AT1-receptor antagonists Irbesartan and Losartan, which are antagonists not only at the AT1R, but also at thromboxane TP-receptors, we tested the hypothesis that C21 has TP-receptor antagonistic properties as well. Isolated mouse mesenteric arteries from C57BL/6 J and AT2R-knockout mice (AT2R-/y) were mounted in wire myographs, contracted with either phenylephrine or the thromboxane A2 (TXA2) analogue U46619, and the relaxing effect of C21 (0.1 nM - 10 µM) was investigated. The effect of C21 on U46619-induced platelet aggregation was measured by an impedance aggregometer. Direct interaction of C21 with TP-receptors was determined by an β-arrestin biosensor assay. C21 caused significant, concentration-dependent relaxations in phenylephrine- and U46619-contracted mesenteric arteries from C57BL/6 J mice. The relaxing effect of C21 was absent in phenylephrine-contracted arteries from AT2R-/y mice, whereas it was unchanged in U46619-contracted arteries from AT2R-/y mice. C21 inhibited U46619-stimulated aggregation of human platelets, which was not inhibited by the AT2R-antagonist PD123319. C21 reduced U46619-induced recruitment of β-arrestin to human thromboxane TP-receptors with a calculated Ki of 3.74 µM. We conclude that in addition to AT2R-agonistic properties, C21 also acts as low-affinity TP-receptor antagonist, and that – depending on the constrictor – both mechanisms can be responsible for C21-induced vasorelaxation. Furthermore, by acting as a TP-receptor antagonist, C21 inhibits platelet aggregation. These findings are important for understanding potential off-target effects of C21 in the preclinical and clinical context and for the interpretation of C21-related myography data in assays with TXA2-analogues as constrictor. [Display omitted] •The established angiotensin AT2-receptor agonist C21 is a low-affinity thromboxane TP-receptor antagonist.•C21 relaxes resistance arteries in TP-receptor and AT2-receptor dependent ways.•C21 inhibits beta-arrestin recruitment to TP-receptors.•C21 inhibits platelet aggregation in a TP-receptor dependent way.•Knowledge of the TP-receptor antagonistic effect of C21 is important to avoid data misinterpretation.