Conditioned Medium of Mesenchymal Stem Cells: Application in Mares with Endometrial Fibrosis

The use of stem cells to promote tissue regeneration has increased in recent years mainly due to their role in growth, remodeling, and repair processes, increasing the number of progenitor cells in the affected tissue. Conditioned medium, a by-product containing metabolites, growth factors, and extracellular matrix proteins is secreted by cultured stem cells. This conditioned medium has been used as a cell-free therapy in regenerative medicine. The objective of the present study was to evaluate the effect of mesenchymal stem cell conditioned medium on endometrial fibrosis in mares through histopathological evaluation. The selected mares had an average age of 18.61 ± 5.68 years and a history of no foaling in the last two breeding seasons. They were grouped according to the degree of uterine fibrosis described by Kenney in 1978: Grade II (n=4), Grade III (n=2). All mares underwent evaluation of vulvar conformation, complete gynecological examination, and ultrasonographic evaluation of the reproductive tract, as well as uterine cytological, bacteriological, and histopathological examinations. The conditioned medium was made from the culture of stem cells derived from the adipose tissue of the lumbarregion of a young horse. During diestrus, using an artificial insemination pipette, 20 mL of conditioned medium was infused into the uterus of each mare, divided into 10 mL per uterine horn. After applying the medium to a horn, 5 mL of sterile 0.9% NaCl solution was administered to ensure that the conditioned medium was infused. Twenty-one days after treatment with the conditioned medium, the six mares were submitted to a new collection of uterine biopsies for histopathological evaluation. In this second evaluation, the same changes characteristic of endometrosis were observed in the histopathology, such as nests with glandular dilation and the presence of areas of fibrosis. These findings suggest that, although no improvement was observed in the histopathological characteristics of endometrial biopsies, the use of the conditioned medium of stem cells did not induce an inflammatory reaction following its intrauterine use, suggesting its safety for further studies in equine medicine. In conclusion, the application of 20 mL of conditioned medium from stem cells in the uterine lumen of six mares with endometrosis grades II and III did not induce endometrial regeneration in the evaluated period.