Effect of rat mesenchymal stem cells on development of abdominal adhesions after surgery

One of the common and most serious side effects of abdominal surgery is the formation of adhesions within the peritoneal cavity during healing. Efforts to prevent adhesion formation have concentrated on inhibiting the inflammatory response, inhibiting the formation or encouraging the lysis of fibrin, and protection of the damaged serosal surface. We are interested in regenerating the serosal surface by providing a source of mesothelial progenitor cells. Rats were divided into groups of 10 each. Abdominal adhesions were created by removing a circle of peritoneum and suturing it back into place. Two weeks later the rats were euthanized and the adhesions scored on a scale of 0-5. A population of mesenchymal stem cells (MSCs) isolated from the skeletal muscle of neonatal rats was tested. The cells were grown in primary culture to expand the population and then trypsinized and frozen at -80 degrees C. They are then thawed and grown in secondary culture before use. The control group were injected with saline i.p. immediately after surgery. The experimental groups received (1) 1.4 X 10(6) MSCs, (2) 5 X 10(6) MSCs, (3) 7.5 X 10(6) dead MSCs, (4) 5 X 10(6) rat smooth muscle cells immediately post-op, and (5) 5 X 10(6) MSCs 4-6 hours after surgery. Only live MSCs given immediately after surgery by i.p. injection significantly decreased the adhesion scores of the rats (mean score of 3.5 vs 0.9). MSCs injected i.p. 4-6 hours after surgery actually increased the adhesion scores (3.5 vs 4.7), and rat smooth muscle cells injected i.p. immediately after surgery had no effect on adhesions. The exact mechanism of action of the MSCs is unknown at this time. However, we postulate that the MSCs have the capacity to differentiate into mesothelial cells capable of repopulating the injured mesothelium.