Objective To investigate the effects of loganin regulating macrophage polarization on the progression of osteoarthritis (OA) and its possible mechanism.

Methods Thirty rats were randomly divided into the sham operation group, OA group and loganin + OA group, with 10 rats in each group. The bone mineral density (BMD) and bone mineral content (BMC) were measured by micro-CT. The pathological damage of cartilage and synovial tissue were stained with Safranin O, and scored by OARSI. Immunofluorescence staining was used to detect the expression of CD86 and CD163 in synovial tissue. The expression levels of TNF-α protein in cartilage and synovial tissue were detected using immunohistochemical staining. The protein expression levels of IL-6 and IL-1β were detected by Western blot.

Results Compared with the sham-operated group, the osteoporosis in the knee joint was found, BMD and BMC decreased (P ＜ 0.05), the knee cartilage damage thinned, the knee surface fissure increased, the chondrocytes neatly arranged, the OARSI score increased (P ＜ 0.05). the expression levels of M1 macrophage marker protein CD86 and M2 macrophage marker protein CD163 in the synovial tissue increased, and the expression levels of TNF-α, IL-6, and IL-1β in the cartilage and synovial tissue increased (P ＜ 0.05). Compared with the OA group, the osteoporosis in the knee joint was improved, the BMD and BMC decreased (P ＜ 0.05), the knee cartilage injury was improved, the chondrocytes were arranged more neatly, the OARSI score decreased (P ＜ 0.05), the CD86 expression in synovial tissue decreased, the CD163 expression increased, and the protein expression levels of TNF-α, IL-6 and IL-1β in cartilage and synovial tissues decreased in the logain + OA group (P ＜ 0.05).

Conclusions Loganin can improve knee joint injury in OA rats by promoting M2 macrophage polarization.