Osteoarthritis (OA) is a degenerative joint disease with an obviously increasing morbidity as age increases, which seriously affects old people’s joint function and life quality. The key to pathological changes in OA is the damage and loss of articular cartilage. Inflammatory cytokines, such as interleukin-1β (IL-1β), could induce cartilage degeneration and inflammatory reaction through a series of cascade reactions, especially in cartilage lesions. Theaflavins (TFs) are the main active ingredients of black tea polyphenols with anti-inflammation and antioxidant functions. This study focuses on the protective effects of TFs against inflammatory degeneration of rat chondrocytes and evaluates the feasibility of TFs in the treatment of OA. 
Male Sprague-Dawley rat’s knee articular chondrocytes were isolated and cultured in vitro, which were identified by toluidine blue staining and type Ⅱ collagen immunofluorescence staining. To select the concentration levels of TFs, cell viability was analyzed with a cell counting kit-8 (CCK-8) assay. Three groups were set in this experiment according to different cultures: blank control group G₀, model group G₁ (10 ng/mL IL-1β) and TFs group G₂ (different concentrations of TFs+10 ng/mL IL-1β). The changes in the mRNA expression levels of two anabolic factors Col Ⅱ (type Ⅱ collagen) and ACAN (aggrecan), the main catabolic factors MMP-13 (matrix metalloproteinases-13), IL-1β, and COX-2 (cyclooxygenase-2) in rat chondrocytes were detected by quantitative real-time polymerase chain reaction (qRT-PCR).
It can be found from the inverted phase contrast microscopy that IL-1β obviously impaired normal rat chondrocyte morphology. It can be seen from the fluorescent microscope that the cell nucleus was stained to be blue and cytoplasm was stained to be green by type Ⅱ collagen immunofluorescence staining, and the extracellular matrix of cells was stained to be blue-purple by toluidine blue staining, which means the cultured cells in the experiment are chondrocytes. The CCK-8 assay indicated that 100 μg/mL TFs significantly decreased the cell viability of normal rat chondrocytes (P＜0.05), but 0-75 μg/mL TFs had no significant cytotoxicity to chondrocytes. The results of qRT-PCR showed that compared with the control group, the mRNA expression levels of chondrocyte markers (Col Ⅱ and ACAN) were obviously down-regulated in the model group (P＜0.01), and the mRNA expression levels of MMP-13, IL-1β and COX-2 increased obviously in the model group (P＜0.05). For the changes, however, the gene expressions of these inflammatory related factors were significantly inhibited by TFs in a dose-dependent manner compared with the model group (P＜0.05).
In conclusion, TFs could effectively alleviate the inflammatory degeneration of rat chondrocytes, via up-regulating anabolic activity, down-regulating catabolic activity and inhibiting inflammatory reaction, so as to protect rat chondrocyts from OA induced by IL-1β. This study provides the first evidence that TFs can significantly inhibit OA disease progression and exert a palliative effect.