Theaflavin-3,3′-Digallate Inhibits Erastin-Induced Chondrocytes Ferroptosis via the Nrf2/GPX4 Signaling Pathway in Osteoarthritis

There is evidence that osteoarthritis (OA) is associated with ferroptosis which is a kind of lipid peroxidation-related cell death. Theaflavin-3,3′-digallate(TF3), a polyphenol compound extracted from black tea, possesses antioxidative and anti-inflammatory properties, but its effects on chondrocyte ferroptosis in osteoarthritis (OA) remain unclear. Our present study aims at exploring the protective role and underlying mechanisms of TF3 against erastin-induced chondrocyte ferroptosis in OA. In human primary chondrocytes treated with erastin alone or combined with different doses of TF3, cell viability was assessed by MTS. Ferroptosis-related proteins, including Gpx4, HO-1, and FTH1, were detected by western blot. The levels of lipid peroxidation and Fe2(+) were determined by fluorescence staining. Meanwhile, the change of related proteins in the Nrf2/Gpx4 signaling pathway was determined by western blot. siRNA-mediated Nrf2 knockdown and the Gpx4 inhibitor RSL3 were used to explore molecular mechanisms for TF3-induced ferroptosis in OA chondrocyte. The magnetic resonance imaging (MRI), HE staining, Masson's staining, and immunohistochemistry were used to evaluate articular cartilage damages in the rat OA model. The results showed that Gpx4 expression was markedly downregulated in the chondrocytes of OA patients. TF3 reversed erastin-induced ferroptosis of human cultured chondrocytes, lipid ROS, and Fe2(+) production in mitochondria. Moreover, the expression of Gpx4, HO-1, FTH1, and Nrf2 was markedly induced by TF3 in the erastin-treated chondrocytes. The antiferroptotic effect of TF3 was related to enhance Nrf2/Gpx4 signaling pathway. Finally, TF3 inhibited OA progression by alleviating in vivo cartilage damage related to chondrocyte ferroptosis. Thus, TF3 significantly inhibits chondrocyte ferroptosis by activating the Nrf2/Gpx4 signaling pathway, suggesting that TF3 serves as a potential therapeutic supplement for OA treatment.