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, -pro7-angiotensin III (-pro7 Ang III), with >20,000-fold affinity for the AT2R over the AT1R, were compared to 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 (20mg/kg/day) 7-apart and were maintained until 35, whilst control mice were instilled with saline 7-apart and maintained for the same time-period. Sub-groups of BLM-injured mice were then treated on 28 with vehicle (saline), C21 (0.3mg/kg/day) or -pro7 Ang III (0.1mg/kg/day) via 7-subcutaneously implanted osmotic minipumps, or daily from 28-35 via orally-administered pirfenidone (100mg/kg/day). At 35 post-injury, measures of lung fibrosis and compliance were evaluated. Compared to their saline-instilled counterparts, saline-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-1 expression, but reduced lung dynamic compliance at 35 post-injury. Whilst all treatments evaluated attenuated the BLM-induced lung myofibroblast accumulation and TGF-1 expression, AT2R stimulation, but not pirfenidone, attenuated lung collagen deposition after 7--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.