The protective effect of phloretin in osteoarthritis: an in vitro and in vivo study

Osteoarthritis (OA) is a degenerative joint disease characterized by the degradation and inflammation of cartilage. Phloretin, a type of dihydrochalcone mainly found in apples and apple-derived products, has been reported to possess various potent biological effects such as antioxidant, anticancer, anti-inflammatory, and immunomodulatory. However, the anti-inflammatory effects of phloretin on OA have not been reported. This study was aimed at assessing the effects of phloretin on human OA chondrocytes. Human OA chondrocytes were pretreated with phloretin (10, 30, and 100 μM) for 2 h and subsequently stimulated with IL-1β for 24 h. The production of NO, PGE2, TNF-α, and IL-6 was determined using the Griess reagent and ELISAs. The mRNA expression of COX-2, iNOS, MMP-3, MMP-13, and ADAMTS-5 was measured by real-time PCR. Changes in the protein expression of COX-2, iNOS, MMPs, ADAMTS, aggrecan, collagen-II, NF-κB, and the PI3K/Akt signaling pathway were detected by western blotting. In this study, we found that phloretin significantly inhibited the IL-1β-induced production of NO, PGE2, TNF-α, and IL-6, the expression of COX-2, iNOS, MMP-3, MMP-13, and ADAMTS-5, and the degradation of aggrecan and collagen-II in human OA chondrocytes. Furthermore, phloretin dramatically suppressed the IL-1β-stimulated phosphorylation of PI3K/Akt and activation of NF-κB in human OA chondrocytes. In addition, treatment with phloretin not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in a mouse model of OA. Moreover, immunohistochemical results showed that phloretin significantly decreased the expression of MMP-13 and increased the expression of collagen-II in OA in mice. In conclusion, these results suggest that phloretin may be a potential agent for the treatment of OA.