Therapeutic efficacy of thrombin-preconditioned mesenchymal stromal cell-derived extracellular vesicles on Escherichia coli-induced acute lung injury in mice.

Background: Acute lung injury (ALI) following pneumonia involves uncontrolled inflammation and tissue injury, leading to high mortality. We previously confirmed the significantly increased cargo content and extracellular vesicle (EV) production in thrombin-preconditioned human mesenchymal stromal cells (thMSCs) compared to those in naïve and other preconditioning methods. This study aimed to investigate the therapeutic efficacy of EVs derived from thMSCs in protecting against inflammation and tissue injury in an Escherichia coli (E. coli)-induced ALI mouse model.

Methods: In vitro, RAW 264.7 cells were stimulated with 0.1 µg/mL liposaccharides (LPS) for 1 h, then were treated with either PBS (LPS Ctrl) or 5 × 10⁷ particles of thMSC-EVs (LPS + thMSC-EVs) for 24 h. Cells and media were harvested for flow cytometry and ELISA. In vivo, ICR mice were anesthetized, intubated, administered 2 × 10⁷ CFU/100 µl of E. coli. 50 min after, mice were then either administered 50 µL saline (ECS) or 1 × 10⁹ particles/50 µL of thMSC-EVs (EME). Three days later, the therapeutic efficacy of thMSC-EVs was assessed using extracted lung tissue, bronchoalveolar lavage fluid (BALF), and in vivo computed tomography scans. One-way analysis of variance with post-hoc TUKEY test was used to compare the experimental groups statistically.

Results: In vitro, IL-1β, CCL-2, and MMP-9 levels were significantly lower in the LPS + thMSC-EVs group than in the LPS Ctrl group. The percentages of M1 macrophages in the normal control, LPS Ctrl, and LPS + thMSC-EV groups were 12.5, 98.4, and 65.9%, respectively. In vivo, the EME group exhibited significantly lower histological scores for alveolar congestion, hemorrhage, wall thickening, and leukocyte infiltration than the ECS group. The wet-dry ratio for the lungs was significantly lower in the EME group than in the ECS group. The BALF levels of CCL2, TNF-a, and IL-6 were significantly lower in the EME group than in the ECS group. In vivo CT analysis revealed a significantly lower percentage of damaged lungs in the EME group than in the ECS group.

Conclusion: Intratracheal thMSC-EVs administration significantly reduced E. coli-induced inflammation and lung tissue damage. Overall, these results suggest therapeutically enhanced thMSC-EVs as a novel promising therapeutic option for ARDS/ALI.