Role of Mesenchymal Stem Cells Exosomes in Lipopolysaccharide-induced Acute Lung Injury in Rats, A Histological Study

Abstract Background Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) represent a substantial disease burden in terms of both morbidity and mortality. And since 2019 this condition represented the leading cause of mortality in patients with severe COVID-19. Mesenchymal stem cells (MSCs) and their exosomes have shown promising results in the modulation of inflammatory responses. Exosomes, have been offering a powerful cell-free therapeutic modality, bypassing most of the safety concerns related to cell-based therapy. Lipopolysaccharide (LPS), a glycoprotein present in the cell wall of gram negative bacteria, could induce ALI in experimental animals, mimicking ARDS in humans. Aim Histological assessment of the potential role of exosomes derived from bone marrow MSCs in treatment of LPS-induced acute lung injury model in adult male albino rats. Materials & Methods Thirty-five rats were used including 5 young aged albino rats that were sacrificed to harvest their bone marrow-derived MSCs and their exosomes. The remaining 30 adult male albino rats were divided into 3 groups. Group I (control group), Group II (LPS group): received a single intraperitoneal injection of LPS dissolved in PBS (6mg/kg). Group III (LPS+Exosomes group): received LPS as in group II followed by intravenous injection of Exosomes (30uL/rat), one hour later. Twenty-four hours later, lung specimens were processed for light & electron microscopic examination, as well as morphometric and statistical analysis. Results H&E-stained sections of Group II revealed marked inflammatory changes as interalveolar septa were significantly thickened by infiltrating inflammatory cells and extravasated red blood cells. Many alveoli appeared narrowed and collapsed while other alveolar spaces were dilated with destruction of the alveolar walls. Blood vessels were congested with thickened walls. The lining epithelium of bronchioles appeared occasionally desquamated and necrotic. Masson’s Trichrome-stained sections showed an apparent increase of collagen fibers around the bronchioles and in the interalveolar septa. Immunohistochemical stain showed a significantly increased reaction to iNOS antibodies in addition to a significantly increased Caspase-3 immune reactivity. Examination with Transmission electron microscopy showed Type I Pneumocyte having an electron dense nucleus and cytoplasmic vacuolations. Type II pneumocytes had degenerated lamellar bodies, many lysosomes and lost microvilli. Eosinophils were seen infiltrating the interstitium with their bilobed nucleus and specific granules with crystalline cores in addition to macrophages with large eccentric nucleus and many lysosomes. On the other hand, the lung structure in Group III showed significant improvement in all parameters. Conclusion The study showed that MSCs exosomes could help in treatment of ALI caused by LPS in rats. Group II showed signs of inflammation and lung damage in addition to increased inflammatory and apoptotic immune reactivity. However, in Group III, treatment with exosomes resulted in significant improvement in all previous parameters. This study highlights the potential of using mesenchymal stem cell exosomes as a treatment for ALI in animals and as a clinical trial.