Impact of MSCs against Hepatic I/R Injury Figure 6. Histopathological changes and Suzuki Score. Hematoxylin eosin staining of I/R-injured liver sections from the MSC group (A. left panel) and the Control group (B. right panel). C. The lower levels of congestion, vacuolization, and necrosis were seen in the MSC group. Suzuki scores = (MSC group vs. Control group: 1.461.3 vs. 3.961.7, p,0.03). doi:10.1371/journal.pone.0019195.g006 Fatal complications in patients receiving major hepatectomy by the Pringle maneuver or by liver transplantation with small-for- size grafts can be reduced by minimizing hepatic I/R injury and avoiding the progress of harmful events following I/R injury. New animal model In the present study, our rat model provided the ideal animal model to research I/R injury after major hepatectomy by the Pringle maneuver or liver transplantation with small-for-size grafts. Intestinal congestion was avoided during the application Figure 7. Remnant liver volume changes. The liver regeneration rate is expressed as remnant liver weight/estimated whole liver weight. doi:10.1371/journal.pone.0019195.g007 of hepatic ischemia by bypassing portal flow through nonischemic lobes (right and caudate lobes). Moreover, the left lateral and the left portion of the medial lobes as well as the nonischemic lobes were excised at the onset of reflow to mimic the clinical condition of liver transplantation with small-for-size grafts or major hepatectomy by the Pringle maneuver in order to research postischemic liver functions. The optimal route of transplantation and the optimal number of MSCs We selected the portal vein as the route for MSC transplan- tation. Systemically transplanted MSC photons were monitored using IVISTM, and were mostly trapped in the microvasculature of the lung because of their size and adhesion potential. Moreover, the MSC-derived photons from the lung faded out within 1 day, and no photons in the I/R-injured liver were detected (data not shown). It is unlikely that recirculating MSCs after pulmonary trapping migrated to the I/R-injured liver. Thus, the systemic route is not always considered the best route for MSC transplantation despite the migration potential of MSCs. A better method for MSC delivery to the liver might be through the portal vein. The optimal number of MSCs is a critical factor, yet little is known about the optimal cell dose. Most reports have used doses of 2 to 10 million MSCs per kilogram in small animal experiments [11]. Some reports have shown that the greater the dose of MSCs transplanted, the greater the therapeutic effect that is achieved. However, the maximum dose in rats and mice is determined by the number of cells that do not undergo fatal embolism by transplantation (usually not more than 10 million cells overall). PLoS ONE | www.plosone.org 5 April 2011 | Volume 6 | Issue 4 | e19195