Exosomes released from human umbilical cord mesenchymal stem cells (hucMSCs) induced an accelerated acute kidney injury (AKI) rat recovery. (A) Blood urea nitrogen (BUN) and creatinine (Cr) values from 0 days to 5 days. At 24 h after cisplatin administration, rats received a renal capsule injection of 200 μg of exosomes from hucMSCs per kidney. Analysis of variance (ANOVA) with two-way classification was performed: *P <0.001, phosphate-buffered saline (PBS) group vs normal group; #P <0.001, hucMSC-ex group vs PBS group. Results showed that BUN and Cr levels were significantly lower in the hucMSC-ex group than in the PBS, hucMSC-CM, non-hucMSC-ex and human lung fibroblast secreted exosomes (HFL-1-ex) groups from 3 days to 5 days. There were no marked changes in the PBS, hucMSC-CM, non-hucMSC-ex and HFL-1-ex groups. (B) Representative micrographs of renal histology at day 5 in the four groups. There were numerous examples of necrosis of the proximal epithelium and tubular protein casts in the PBS, hucMSC-CM, non-hucMSC-ex and HFL-1-ex groups, but this was not the case in the hucMSC-ex group. Original magnification, × 200. Scale bars: 100 μm. Group, n = 6. (C) Incorporation of hucMSC-ex in tubular epithelial cells by renal capsule injection: (a) unlabeled hucMSC-ex was injected into the kidney, no red fluorescence was detected; (b) red fluorescence (white arrows) was observed in the tubular epithelial cells after injection of CM-Dil dye-labeled hucMSC-ex at 24 h. Tubular epithelial cell cytoplasm and nuclei were stained green and blue, respectively. Original magnification × 200.