Amygdalin and magnesium ions exert synergistic effects on cartilage regeneration by inhibiting chondrocyte ferroptosis via the IL-17/GPX4 axis

Cartilage defects (CDs) present a significant challenge in orthopaedic medicine. Owing to the inherently limited regenerative capacity of cartilaginous tissue, defects usually do not heal via natural repair processes. Consequently, damaged tissue is replaced by fibrocartilage-like tissues instead of the original hyaline cartilage. Therefore, inhibiting fibrocartilage formation while promoting hyalinisation may represent a novel strategy for CD therapy. Although studies have explored the role of interleukin (IL)-17A and ferroptosis in the fibrosis of visceral organs, such as the liver, lungs, and kidneys, their implication in cartilage fibrosis and fibrocartilage formation remains unclear. Herein, we aimed to determine whether IL-17A and ferroptosis are collectively involved in the process of cartilage fibrosis and to investigate the effects of amygdalin (AMD) and magnesium ions (Mg2+) in cartilage regeneration and the potential molecular mechanisms underlying these effects. Cartilage samples were collected from patients with osteoarthritis and subjected to immunohistochemistry analysis to assess fibrocartilage formation indicators within the degenerated areas. Quantitative real-time polymerase chain reaction, western blot, and immunohistochemistry analyses were employed to assess changes in cartilage anabolism and expression of fibrocartilage markers after treatment with different concentrations of AMD. We also treated chondrocytes with an IL-17A/RA antagonist, a ferroptosis inhibitor, a ferroptosis inducer, and AMD, and measured the changes in fibrocartilage-, ferroptosis-, and IL-17 signalling-associated factors. Finally, mice with microfracture (MF)-induced CDs were administered intra-articular injections of either saline, AMD (10 μmol/L), MgCl2 (0.5 mmol/L), or AMD (10 μmol/mL) plus MgCl2 (0.5 mmol/L) twice a week. After 4 and 8 weeks, chondral repair was assessed through histological and immunohistochemical analyses in each group. IL-17A activated lipid peroxidation, leading to chondrocyte ferroptosis, while AMD suppressed IL-17 signalling, thereby mitigating the decrease in glutathione peroxidase 4 (GPX4) expression induced by IL-17A or erastin. In mice with MF surgery-induced CD, the combination of AMD and Mg2+ mitigated oxidative stress, thereby enhancing the positive effects of Mg2+. This combination led to a significant improvement in chondrogenesis, activation of anabolic processes, and reduction of catabolic activity in the articular cartilage, ultimately supporting cartilage repair and regeneration. AMD targets IL-17 signalling to inhibit chondrocyte ferroptosis. Furthermore, the combination of AMD and Mg2+ suppresses IL-17A/GPX4 signalling, suppressing fibrocartilage formation and fostering hyaline cartilage regeneration. In the present study, we showed that IL-17A may represent a promising therapeutic target for cartilage repair and regeneration. A conservative therapeutic strategy involving joint injections of AMD (a natural plant extract) and Mg2+ (a crucial endogenous factor that promotes chondrogenesis) facilitated effective cartilage repair and regeneration. This strategy represents a cost-effective approach with potential for clinical application.