OBJECTIVE  To study the effect of Netrin-1 mediated sensory neural sprouting on pain behavior in knee osteoarthritis (KOA) rats and the intervention effect of warming meridians and invigorating blood external treatment.

  METHODS  30 rats were randomly divided into the blank group, KOA group, and external treatment group. The KOA model was constructed by the anterior cruciate ligament transaction (ACLT). After successful modeling, the external treatment group was applied with the representative formula of warming meridians and invigorating blood external treatment, Easy Layer, for 28 days. After administration, blood was collected from the abdominal aorta of each rat; synovial tissue and dorsal root ganglia (DRG) tissue were extracted from each group. Hematoxylin eosin staining (HE) was used to observe synovial inflammation; nerve silver staining was used to observe nerve sprouting in synovium; ELISA was used to detect the levels of inflammatory factor interleukin 6 (IL-6), pain factors substance p (SP) and Calcitonin gene related peptide (CGRP) in serum; western blot and qPCR were used to detect protein and gene levels of Netrin-1 and CGRP in synovial tissue and deleted in colorectal cancer (DCC), uncoordinated homology-5 (UNC5) of neuronal surface receptors in DRG tissue.

  RESULTS  HE staining showed a significant decrease in inflammatory cell infiltration in the external treatment group compared to the KOA group; nerve silver plating showed a significant decrease in the number of nerve fibers in the external treatment group compared to the KOA group. The content of IL-6 and SP in the KOA group was significantly increased compared to the blank group, while the content of IL-6 and SP in the external treatment group was significantly reduced compared to the KOA group. The protein and gene expression of Netrin-1, CGRP, DCC was significantly increased and UNC5 was reduced in the KOA group compared to the blank group; the protein and gene expression of Netrin-1, CGRP, DCC was significantly reduced and UNC5 was increased in the external treatment group compared to the KOA group.

  CONCLUSION  The external therapy of warming meridians and invigorating blood can alleviate KOA pain, and the mechanism may be related to the inhibition of Netrin-1-mediated sensory nerve sprouting and the reduction of pain mediator secretion.