Relative affinity of angiotensin peptides and novel ligands at AT1 and AT2 receptors

AT(1)R (angiotensin type 1 receptor) and AT(2)R (angiotensin type 2 receptor) are well known to be involved in the complex cardiovascular actions of AngII (angiotensin II). However, shorter peptide fragments of AngII are thought to have biological activity in their own right and elicit effects that oppose those mediated by AngII. In the present study, we have used HEK (human embryonic kidney)-293 cells stably transfected with either AT(1)R or AT(2)R to perform a systematic analysis of binding affinities of all the major angiotensin peptides. Additionally, we tested the novel AT(2)R agonist Compound 21, as well as the MasR (Mas receptor) agonist and antagonist AVE0991 and A-779 respectively, for their ability to bind to AT, R or AT(2)R. Candesartan, CGP42214 and PD123319 were used as reference compounds. Binding studies using I-125- [Sar(1)lle(8)]AngII on the AT(1)R-transfected HEK-293 cells revealed only AngII, AngIII [angiotensin III; angiotensin-(2-8)] and candesartan to have high affinity for AT, R. In the AT(2)R-transfected HEK-293 cells, competition for I-125-[Sar(1)lle(8)]AngII binding was observed for all ligands except candesartan, AVE0991 and A779, the latter two compounds having negligible affinity at either AT(1)R or AT(2)R. The rank order of affinity of ligands at AT(2)R was CGP42112>AngII >= AngIII>Compound 21 >= PD123319 >> AngIV [angiotensin IV; angiotensin-(3-8)]>Ang-(1-7) [angiotensin-( 1-7)]. Of note, although AngIV and Ang-( 1-7) exhibited only modest affinity at AT(2)R compared with AngII, these two angiotensin peptides, together with AngIII, had substantial AT(2)R selectivity over AT(1)R. Collectively, our results suggest that shorter angiotensin peptides can act as endogenous ligands at AT(2)R.