To observe any effect of exosomes derived from umbilical cord mesenchymal stem cells on pain, cartilage repair and the expression of transcriptional activator 3 (ATF-3) and growth related protein 43 (GAP-43) in the dorsal root ganglia (DRG), as well as to explore the mechanism of their relieving pain.

Fifty-four male Sprague-Dawley rats were randomly divided into a sham-operation group, a monoiodoacetate group and an exosome group, each of 18. The knee cavities of the left hind limbs of all of the rats except those in the sham-operation group were injected with 50μl of monoiodoacetate to establish an arthritis pain model. The sham-operation group received only 50μl of saline solution as controls. Two weeks after the modelling, the knee joint cavities of the exosome group were injected with 50μl of exosomes, while the other two groups were injected with 50μl of normal saline. The rats′ mechanical and thermal pain thresholds were measured 1 day before the modeling, 7 and 14 days after the monoiodoacetate injection, as well as 7, 14 and 28 days after the exosome injection. Western blotting was used to detect the expression of ATF-3 and GAP-43 in the rats′ DRG, while hematoxylin and eosin staining was used to detect any cartilage repair.

Compared with the monoiodoacetate group, the latency of the mechanical and thermal pain thresholds had increased significantly in the exosome group 7 days after the exosome injection. The difference remained significant until the 28th day after the injection. The expression of ATF-3 protein decreased significantly and that of the GAP-43 protein increased significantly. Significant differences were observed in the average Osteoarthritis Research Society International (OARSI) knee cartilage score.

Exosomes can alleviate the pain induced by monoiodoacetate adjuvant. The analgesic mechanism may be related to reducing nerve injury and promoting nerve and cartilage repair, with the nerve repair earlier than cartilage repair.

Exosomes; Activating transcription factors; Growth associated protein; Cartilage repair; Neuropathic pain