Therapeutic potential of mesenchymal stem cells in acute kidney injury is affected by administration timing

: Mesenchymal stem cell (MSC) transplantation is a promising therapy for acute kidney injury; however, the efficacy is limited due to poor survival after transplantation. In this study, we investigated how MSC transplantation timing affected the survival and therapeutic potential of MSCs in the kidney ischemia-reperfusion (I/R) injury model. After kidney I/R injury, the inflammatory process and tissue damage were characterized over 1 week post-I/R, we found that inflammation peaked at 12-24 h post-I/R (h.p.i.), and urine  neutrophil gelatinase-associated lipocalin (NGAL) measurements correlated highly with measures of inflammation. We cultured MSCs with supernatants from I/R injured kidney tissue homogenates collected at different time points and found that kidney homogenates from 12 and 24 h.p.i. were most toxic to MSCs, whereas homogenates from 1 h.p.i. were not as cytotoxic as those from 12 and 24 h.p.i. Compared with MSCs administered at 12, or 24 h.p.i., cells administered immediately after ischemia or 1 h.p.i. yielded the highest renoprotective and anti-inflammatory effects. Our findings indicate that MSC treatment for acute kidney injury is most effective when applied prior to the development of a potent inflammatory microenvironment, and urine NGAL may be helpful for detecting inflammation and selecting MSC transplantation timing in I/R kidney injury.