The first druglike selective angiotensin II AT(2) receptor agonist (21) with a K(i) value of 0.4 nM for the AT(2) receptor and a K(i) > 10 microM for the AT(1) receptor is reported. Compound 21, with a bioavailability of 20-30% after oral administration and a half-life estimated to 4 h in rat, induces outgrowth of neurite cells, stimulates p42/p44(mapk), enhances in vivo duodenal alkaline secretion in Sprague-Dawley rats, and lowers the mean arterial blood pressure in anesthetized, spontaneously hypertensive rats. Thus, the peptidomimetic 21 exerts a similar biological response as the endogenous peptide angiotensin II after selective activation of the AT(2) receptor. Compound 21, derived from the prototype nonselective AT(1)/AT(2) receptor agonist L-162,313 will serve as a valuable research tool, enabling studies of the function of the AT(2) receptor in more detail.

Background-This study is the first to examine the effect of direct angiotensin II type 2 (AT 2 ) receptor stimulation on postinfarct cardiac function with the use of the novel nonpeptide AT 2 receptor agonist compound 21 (C21). Methods and Results-Myocardial infarction (MI) was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with C21 (0.01, 0.03, 0.3 mg/kg per day IP) was started 24 hours after MI and was continued until euthanasia (7 days after MI). Infarct size was assessed by magnetic resonance imaging, and hemodynamic measurements were performed via transthoracic Doppler echocardiography and intracardiac Millar catheter. Cardiac tissues were analyzed for inflammation and apoptosis markers with immunoblotting and real-time reverse transcription polymerase chain reaction. C21 significantly improved systolic and diastolic ventricular function. Scar size was smallest in the C21-treated rats. In regard to underlying mechanisms, C21 diminished MI-induced Fas-ligand and caspase-3 expression in the peri-infarct zone, indicating an antiapoptotic effect. Phosphorylation of the p44/42 and p38 mitogen-activated protein kinases, both involved in the regulation of cell survival, was strongly reduced after MI but almost completely rescued by C21 treatment. Furthermore, C21 decreased MI-induced serum monocyte chemoattractant protein-1 and myeloperoxidase as well as cardiac interleukin-6, interleukin-1␤, and interleukin-2 expression, suggesting an antiinflammatory effect. Conclusions-Direct

Abstract-Angiotensin II type 2 (AT 2 ) receptors can be regarded as an endogenous repair system, because the AT 2 receptor is upregulated in tissue damage and mediates tissue protection. A potential therapeutic use of this system has only recently come within reach through synthesis of the first selective, orally active, nonpeptide AT 2 receptor agonist, compound 21 (C21; dissociation constant for AT 2 receptor: 0.4 nM; dissociation constant for angiotensin II type 1 receptor: Ͼ10 000 nM). This study tested AT 2 receptor stimulation with C21 as a potential future therapeutic approach for the inhibition of proinflammatory cytokines and of nuclear factor B. C21 dose-dependently (1 nM to 1 mol/L) reduced tumor necrosis factor-␣-induced interleukin 6 levels in primary human and murine dermal fibroblasts. AT 2 receptor specificity was controlled for by inhibition with the AT 2 receptor antagonist PD123319 and by the absence of effects in AT 2 receptor-deficient cells. AT 2 receptor-coupled signaling leading to reduced interleukin 6 levels involved inhibition of nuclear factor B, activation of protein phosphatases, and synthesis of epoxyeicosatrienoic acid. Inhibition of interleukin 6 promoter activity by C21 was comparable in strength to inhibition by hydrocortisone. C21 also reduced monocyte chemoattractant protein 1 and tumor necrosis factor-␣ in vitro and in bleomycin-induced toxic cutaneous inflammation in vivo. This study is the first to show the anti-inflammatory effects of direct AT 2 receptor stimulation in vitro and in vivo by the orally active, nonpeptide AT 2 receptor agonist C21. These data suggest that pharmacological AT 2 receptor stimulation may be an orally applicable future therapeutic approach in pathological settings requiring the reduction of interleukin 6 or inhibition of nuclear factor B. (Hypertension. 2010;55:924-931.)