Abstract: Objective　This study was intended to evaluate the protective effects of psoralen against Leptin-induced catabolic responses in human chondrocytes in vitro; elucidate the underlying molecular mechanism in general and the PI3K-AKT-NF- κB signaling axis in particular and validate the in vivo efficacy of psoralen in a surgically induced rat model of osteoarthritis.Methods　 Clinical specimens of knee joints from osteoarthritis patients and modeled rats were collected to detect expression levels of leptin via immunofluorescence. Articular chondrocytes of human knees were isolated, cultured, and identified. The appropriate concentration of psoralen under 100 ng/mL leptin stimulation was screened using the cell counting kit-8 (CCK‑8) assay and immunofluorescence staining for matrix metalloproteinase 13 (MMP13). Protein expression levels of phosphatidylinositol 3-kinase/phosphorylated phosphatidylinositol 3-kinase (PI3K/p-PI3K), protein kinase B/phosphorylated protein kinase B (AKT/p-AKT), nuclear factor- κB p65 subunit/phosphorylated p65 subunit (p65/p-p65), MMP13, and collagen type Ⅱ (Col2) were detected by Western blotting (WB). Forty specific-pathogen-free (SPF) -grade Sprague-Dawley (SD) rats were randomly divided into five groups : the sham‑operation group, model group, low‑dose psoralen group (5 mg/kg), medium‑dose group (10 mg/kg), and high‑dose group (20 mg/kg). A rat osteoarthritis model was established via anterior cruciate ligament transection (ACLT). After modeling, the rats were intragastrically administered with the corresponding concentration of psoralen for four consecutive weeks, while the sham and model groups received an equal volume of saline. CatWalk gait analysis system was used to evaluate the functional recovery of lower limbs. Micro‑computed tomography (Micro‑CT) imaging was applied to assess subchondral bone remodeling. Histological staining combined with the Osteoarthritis Research Society International (OARSI) scoring system was performed for semi‑quantitative evaluation of cartilage degradation. Results　Immunofluorescence staining of clinical and animal specimens showed that leptin expression was significantly higher in clinical knee samples with Kellgren-Lawrence (KL) grade 3-4 than in those with KL grade 1-2 (P＜0.001). Leptin expression in the ACLT group was also markedly higher than in the sham group (P＜0.001). In vitro experiments, CCK‑8 assays indicated that psoralen at 5-40 μmol/L had no toxicity on chondrocytes. MMP13 immunofluorescence staining and semi‑quantitative analysis suggested that 20 μmol/L psoralen significantly reduced the rate of MMP13‑positive cells induced by leptin (P＜0.001) and was the optimal concentration for in vitro studies. Western blot analysis showed that, compared with the blank control group, the relative expression levels of p-PI3K, p‑AKT, p‑p65, and MMP13 in the leptin‑stimulated group were significantly increased (P＜0.001) but that of Col2 was significantly decreased (P＜0.001). These changes in protein expression were significantly reversed in the 20 μmol/L psoralen intervention group compared with the leptin-stimulated group (P＜0.001). In vivo experiments, gait analysis found that, compared with the model group, all psoralen dose groups showed significantly increased average intensity, duty cycle, and footprint area of the lower limbs (P＜0.001). Among them, the duty cycle in the 10 mg/kg (P＜0.001) and 20 mg/kg (P＜0.05) groups was significantly higher than in the 5 mg/kg group, but no significant differences were observed in average intensity or footprint areas between the three dose groups (P＞0.05). Micro‑CT analysis indicated that the osteophyte volume in the 5 mg/kg psoralen group was not significantly different from that of the ACLT group (P＞0.05) but trended downward. There were significant decreases in the 10 mg/kg (P＜0.01) and 20 mg/kg (P＜0.05), but there was no significant difference in the osteophyte volume between the three dose groups (P＞0.05). The BV/TV ratio was significantly increased while the Tb.Sp value was significantly decreased, with more pronounced improvement in the 10 mg/kg (P＜0.001) and 20 mg/kg (P＜0.05) groups than in the 5 mg/kg group. Histological staining and OARSI scores showed that, compared with the ACLT group, more complete cartilage extracellular matrixs were retained in each of psoralen dose groups , but OARSI scores were significantly reduced (P＜0.01), especially in the 10 mg/kg (P＜0.001) and 20 mg/kg (P＜0.05) groups. Conclusion　Psoralen can exert chondroprotective effects by inhibiting the catabolic response of chondrocytes induced by Leptin in vitro, thereby exerting a chondroprotective effect. The molecular mechanism may be related to the regulation of the phosphatidylinositol 3-kinase-protein kinase B-nuclear factor- κB pathway (PI3K-AKT-NF- κB). In animal experiments, psoralen can effectively delay the pathological process of osteoarthritis.Background　Leptin has been proved to be involved in the pathogenesis and progression of osteoarthritis , while psoralen has showed chondroprotective potential in preclinical studies. However, whether leptin can serve as a mechanistically relevant therapeutic target for psoralen remains unclear.