The novel AT2 receptor ligand, β-Pro7 Ang III, induces equivalent anti-fibrotic effects to Compound 21 but broader anti-fibrotic effects than pirfenidone in mice with bleomycin-induced pulmonary fibrosis

Angiotensin II AT2 receptor (AT2R) activation leads to significant anti-fibrotic and anti-inflammatory effects in diseased organs, which has led to clinical trial evaluation of the AT2R agonist, Compound 21 (C21), as a treatment for idiopathic pulmonary fibrosis (IPF). In this study, the anti-fibrotic effects of a more selective AT2R ligand, β-Pro7 angiotensin III (β-Pro7 Ang III), with >20,000-fold affinity for the AT2R over the AT1R, were compared with that of C21 or the currently used IPF medication, pirfenidone, in mice with bleomycin (BLM)-induced pulmonary fibrosis. Adult female BALB/c mice received a double intranasal instillation of BLM (20 mg/kg/day) seven days apart and were maintained until day 35, while control mice were instilled with saline (SAL) seven days apart and maintained for the same time period. Sub-groups of BLM-injured mice were then treated on day 28 with vehicle (SAL), C21 (0.3 mg/kg/day) or β-Pro7 Ang III (0.1 mg/kg/day) via seven-day subcutaneously implanted osmotic minipumps, or daily from days 28 to 35 via orally administered pirfenidone (100 mg/kg/day). At day-35 post-injury, measures of lung fibrosis and compliance were evaluated. Compared with their SAL-instilled counterparts, SAL-treated BLM-injured mice presented with a significantly increased lung Ashcroft score, Masson's trichrome-stained and second harmonics generation-measured fibrosis, myofibroblast accumulation, and TGF-β1 expression, but reduced lung dynamic compliance at day-35 post-injury. While all treatments evaluated attenuated the BLM-induced lung myofibroblast accumulation and TGF-β1 expression, AT2R stimulation, but not pirfenidone, attenuated lung collagen deposition after seven days. β-Pro7 Ang III also significantly restored lung compliance and promoted collagen-degrading matrix metalloproteinase-2 activity. These findings highlighted the therapeutic value of selectively targeting the AT2R for treating IPF.