Abstract: Objective:To study the chondroprotective and anti-inflammatory effect of purpurin on osteoarthritis(OA)of the knee in rats.Methods:Chondrocytes from SD rats were extracted in vitro and randomly divided into control, model(IL-1β-treated)and treatment groups(IL-1β and purpurin-treated).The cell counting kit(CCK-8)was used to assess the toxic effect of purpurin on chondrocytes.Chondrocyte viability was assessed by Calcein-AM/Propidium iodide(PI)staining, and ROS levels of chondrocytes were assessed by reactive oxygen species detection assay.Based on Swiss Target Prediction, SuperPred, Sea, GeneCards and OMIM databases, the potential targets of purpurin for knee OA were screened, and molecular docking between purpurin and intersecting targets was performed using AutoDock Vina and Pymol softwares.The relative expressions of inflammation-related and characteristic genes in chondrocytes were mea-sured by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR).Eighteen rats were randomly divided into control, model and treatment groups.Arthritis models were constructed by severing the anterior cruciate ligament in the model and treatment groups.After four weeks of modeling, 100 μL of purpurin solution was injected into the joint cavity of rats in the treatment group and an equal volume of saline in the control and model groups every week.The histopathological conditions of the rat joints were evaluated by HE staining and staining with senna O-fix green.Results:CCK-8 results showed that 50 μmol/L of purpurin was not toxic to chondrocytes and promoted their proliferation (P< 0.001).Calcein-AM/PI staining showed that the number of dead cells was less and the number of live cells also increased in the treatment group compared with the model group(P< 0.01).The results of the reactive oxygen content assay showed that the fluorescence intensity was diminished in the treatment group compared with the model group (P< 0.05).The results of drug target screening and molecular docking suggested that purpurin might affect the progression of OA by regulating the expressions of transthyretin(TTR), B lymphocytoma-2 (BCL2) and matrix metalloproteinase 1 (MMP1).RT-qPCR results showed that the relative expressions of inflammatory genes in the treated group compared with the model group significantly decreased (P< 0.01), while the relative expressions of cartilage-characteristic genes increased in the treatment group (P< 0.001).Histological staining results showed that cartilage tissue damage was reduced in the treatment group compared to the inflammation group.Conclusion:Purpurin has a chondroprotective effect on OA of the knee in rats and reduces the inflammatory response of chondrocytes.It may be a potential drug for the treatment of arthritis.