A Single β-Amino Acid Substitution to Angiotensin II Confers AT2 Receptor Selectivity and Vascular Function
Novel AT2R ligands were designed by substituting individual β-amino acid in the sequence of the native ligand angiotensin II (Ang II). Relative ATR selectivity and functional vascular assays (in vitro AT2R-mediated vasorelaxation and in vivo vasodepressor action) were determined. In competition binding experiments using either AT1R- or AT2R- transfected HEK-293 cells, only β-Asp1-Ang II and Ang II fully displaced [125I]-Ang II from AT1R. In contrast, β-substitutions at each position of Ang II exhibited AT2R affinity, with β-Tyr4-Ang II and β-Ile5-Ang II exhibiting ≈1000-fold AT2R selectivity. In mouse aortic rings, β-Tyr4-Ang II and β-Ile5-Ang II evoked vasorelaxation that was sensitive to blockade by the AT2R antagonist PD123319 and the nitric oxide synthase inhibitor L-NAME. When tested with a low level of AT1R blockade, β-Ile5-Ang II (15 pmol/kg per minute IV for 4 hours) reduced blood pressure (BP) in conscious spontaneously hypertensive rats (β-Ile5-Ang II plus candesartan, −24±4 mm Hg) to a greater extent than candesartan alone (−11±3 mm Hg, n=7, P<0.05), an effect that was abolished by concomitant PD123319 infusion. However, in an identical experimental protocol, β-Tyr4-Ang II had no influence on BP (n=10), and it was less stable than β-Ile5-Ang II in plasma stability assays. Thus, this study demonstrated that a single β-amino acid substitution resulted in a compound that demonstrated both in vitro vasorelaxation and in vivo depressor activity via AT2R. This approach to the design and synthesis of novel AT2R-selective peptidomimetics shows great potential to provide insight into AT2R function.
- Received October 11, 2010.
- Revision received November 3, 2010.
- Accepted December 9, 2010.
- © 2011 American Heart Association, Inc.