Relaxin-Loaded Inhaled Porous Microspheres Inhibit Idiopathic Pulmonary Fibrosis and Improve Pulmonary Function Post-Bleomycin Challenges

Idiopathic pulmonary fibrosis (IPF) causes worseningpulmonaryfunction, and no effective treatment for the disease etiology is availablenow. Recombinant Human Relaxin-2 (RLX), a peptide agent with anti-remodelingand anti-fibrotic effects, is a promising biotherapeutic candidatefor musculoskeletal fibrosis. However, due to its short circulatinghalf-life, optimal efficacy requires continuous infusion or repeatedinjections. Here, we developed the porous microspheres loading RLX(RLX@PMs) and evaluated their therapeutic potential on IPF by aerosolinhalation. RLX@PMs have a large geometric diameter as RLX reservoirsfor a long-term drug release, but smaller aerodynamic diameter dueto their porous structures, which were beneficial for higher depositionin the deeper lungs. The results showed a prolonged release over 24days, and the released drug maintained its peptide structure and activity.RLX@PMs protected mice from excessive collagen deposition, architecturaldistortion, and decreased compliance after a single inhalation administrationin the bleomycin-induced pulmonary fibrosis model. Moreover, RLX@PMsshowed better safety than frequent gavage administration of pirfenidone.We also found RLX-ameliorated human myofibroblast-induced collagengel contraction and suppressed macrophage polarization to the M2 type,which may be the reason for reversing fibrosis. Hence, RLX@PMs representa novel strategy for the treatment of IPF and suggest clinical translationalpotential.