A Single β-Amino Acid Substitution to Angiotensin II Confers AT2 Receptor Selectivity and Vascular Function

Novel AT 2 R 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 AT 2 R-mediated vasorelaxation and in vivo vasodepressor action) were determined. In competition binding experiments using either AT 1 R- or AT 2 R- transfected HEK-293 cells, only β-Asp 1 -Ang II and Ang II fully displaced [ 125 I]-Ang II from AT 1 R. In contrast, β-substitutions at each position of Ang II exhibited AT 2 R affinity, with β-Tyr 4 -Ang II and β-Ile 5 -Ang II exhibiting ≈1000-fold AT 2 R selectivity. In mouse aortic rings, β-Tyr 4 -Ang II and β-Ile 5 -Ang II evoked vasorelaxation that was sensitive to blockade by the AT 2 R antagonist PD123319 and the nitric oxide synthase inhibitor L-NAME. When tested with a low level of AT 1 R blockade, β-Ile 5 -Ang II (15 pmol/kg per minute IV for 4 hours) reduced blood pressure (BP) in conscious spontaneously hypertensive rats (β-Ile 5 -Ang II plus candesartan, −24±4 mm Hg) to a greater extent than candesartan alone (−11±3 mm Hg, n=7, P 4 -Ang II had no influence on BP (n=10), and it was less stable than β-Ile 5 -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 AT 2 R. This approach to the design and synthesis of novel AT 2 R-selective peptidomimetics shows great potential to provide insight into AT 2 R function.