Intratracheal administration of mesenchymal stem cell-derived extracellular vesicles reduces lung injuries in a chronic rat model of bronchopulmonary dysplasia

Early therapeutic effect of intratracheally (IT)-administered extracellular vesicles secreted by mesenchymal stem cells (MSC-EVs) has been demonstrated in a rat model of bronchopulmonary dysplasia (BPD) involving hyperoxia exposure in the first 2 postnatal weeks. The aim of this study was to evaluate the protective effects of IT-administered MSC-EVs in the long term. EVs were produced from MSCs following GMP standards. At birth, rats were distributed in three groups: a) animals raised in ambient air for 6 weeks (n=10); and animals exposed to 60% hyperoxia for 2 weeks and to room air for additional 4 weeks and treated with b) IT-administered saline solution (n=10), or c) MSC-EVs (n=10) on postnatal days 3, 7, 10 and 21. Hyperoxia exposure produced significant decreases in total number of alveoli, total surface area of alveolar air spaces and proliferation index, together with increases in mean alveolar volume, mean linear intercept and fibrosis percentage; all these morphometric changes were prevented by MSC-EVs treatment. The medial thickness index for <100 µm vessels was higher for hyperoxia-exposed/sham-treated than for normoxia-exposed rats; MSC-EV treatment significantly reduced this index. There were no significant differences in interstitial/alveolar and perivascular F4/8-positive and CD86-positive macrophages. Conversely, hyperoxia exposure reduced CD163-positive macrophages both in interstitial/alveolar and perivascular populations and MSC-EV prevented these hyperoxia-induced reductions. These findings furtherly support that IT-administered EVs could be an effective approach to prevent/treat BPD, ameliorating the impaired alveolarization and pulmonary artery remodelling also in a long-term model. M2 macrophage polarization could play a role through anti-inflammatory and proliferative mechanisms.