Regulation of type II collagen, matrix metalloproteinase-13 and cell proliferation by interleukin-1β is mediated by curcumin via inhibition of NF-κB signaling in rat chondrocytes

Curcumin possesses strong anti-inflammatory, anti-rheumatoid and anti-oxidative activities, and has the potential to inhibit nuclear factor‑κB (NF‑κB) signaling. Cartilage damage in osteoarthritis (OA) is largely mediated by interleukin-1β (IL-1β) via activation of various transcription factors, including NF‑κB and activator protein‑1. The aim of the present study was to determine whether IL‑1β induces matrix metalloproteinase-13 (MMP-13) expression and inhibits type II collagen expression, as well as to examine whether cell proliferation may be inhibited by curcumin through the inhibition of NF‑κB signaling. The effects of curcumin were investigated in rat articular chondrocyte cell cultures treated with IL‑1β in the presence or absence of curcumin or the NF‑κB inhibitor pyrrolidine dithiocarbamate. Western blotting and reverse transcription‑quantitative polymerase chain reaction were conducted to evaluate protein and mRNA expression levels of type II collagen, MMP‑13, NF‑κB inhibitor α (IκBα), phosphorylated‑IκBα and NF‑κB subunit p65/RelA. Western blotting and immunofluorescence were performed to examine the effects of curcumin on the expression, phosphorylation and nuclear translocation of NF‑κB‑associated proteins. The effects of curcumin on cell proliferation were evaluated by Cell Counting Kit‑8 (CCK‑8). Curcumin was demonstrated to inhibit the IL‑1β‑induced activation of NF‑κB by suppressing IκBα phosphorylation and p65/RelA nuclear translocation. These events were associated with the downregulation of MMP‑13 expression and the upregulation of type II collagen expression, both of which are considered to be NF‑κB targets. CCK‑8 assays revealed that co‑treatment with curcumin resulted in increased proliferation in IL‑1β‑treated chondrocytes. These findings implicated curcumin as a naturally occurring anti‑inflammatory agent for the treatment of OA via inhibition of NF‑κB signaling.