Osteoarthritis (OA) is characterized by degeneration of articular cartilage. Studies have found that enhancement of autophagy, an intracellular catabolic process, may limit the pathologic progression of OA. Chloramphenicol is a potent activator of autophagy; however, the effects of chloramphenicol on articular cartilage are unknown.
Using human OA knee chondrocytes in vitro, we asked, does chloramphenicol (1) activate autophagy in chondrocytes; (2) protect chondrocytes from IL-1β-induced apoptosis; and (3) reduce the expression of matrix metallopeptidase (MMP)-13 and IL-6 (markers associated with articular cartilage degradation and joint inflammation). Using an in vivo rabbit model of OA, we asked, does an intra-articular injection of chloramphenicol in the knee (4) induce autophagy; (5) reduce OA severity; and (6) reduce MMP-13 expression?
Human chondrocytes were extracted from 10 men with OA undergoing TKA. After treatment with 25 μg/mL, 50 μg/mL, or 100μg/mL chloramphenicol, the autophagy of chondrocytes was detected with Western blotting, transmission electron microscopy, or an autophagy detection kit. There were four groups in our study: one group was untreated, one was treated with 100 μg/mL chloramphenicol, another was treated with 10 ng/mL of IL-1β, and the final group was treated with 10 ng/mL of IL-1β and 100 μg/mL of chloramphenicol. All groups were treated for 48 hours; cell apoptosis was detected with Western blotting and flow cytometry. Inflammation marker IL-6 in the cell culture supernatant was detected with an ELISA. Articular cartilage degradation-related enzyme MMP-13 was analyzed with Western blotting. A rabbit model of OA was induced by intra-articular injection of type II collagenase in 20 male 3-month-old New Zealand White rabbits' right hind leg knees; the left hind leg knees served as controls. Rabbits were treated by intra-articular injection of saline or chloramphenicol once a week for 8 weeks. Autophagy of the articular cartilage was detected with Western blotting and transmission electron microscopy. Degeneration of articular cartilage was analyzed with Safranin O-fast green staining and the semi-quantitative index Osteoarthritis Research Society International (OARSI) grading system. Degeneration of articular cartilage was evaluated using the OARSI grading system. The expression of MMP-13 in articular cartilage was detected with immunohistochemistry.
Chloramphenicol activated autophagy in vitro in the chondrocytes of humans with OA and in an in vivo rabbit model of OA. Chloramphenicol inhibited IL-1-induced apoptosis (flow cytometry results with chloramphenicol, 25.33 ± 3.51%, and without chloramphenicol, 44.00 ± 3.61%, mean difference, 18.67% [95% CI 10.60 to 26.73]; p = 0.003) and the production of proinflammatory cytokine IL-6 (ELISA results, with chloramphenicol, 720.00 ± 96.44 pg/mL, without chloramphenicol, 966.67 ± 85.05 pg/mL; mean difference 74.24 pg/mL [95% CI 39.28 to 454.06]; p = 0.029) in chondrocytes. After chloramphenicol treatment, the severity of cartilage degradation was reduced in the treatment group (OARSI 6.80 ± 2.71) compared with the control group (12.30 ± 2.77), (mean difference 5.50 [95% CI 1.50 to 9.50]; p = 0.013). Furthermore, chloramphenicol treatment also decreased the production of MMP-13 in vitro and in vivo.
Our study suggests that an intra-articular injection of chloramphenicol may reduce degeneration of articular cartilage and that induction of autophagy may be a method for treating OA. The animal model we used was type II collagen-induced OA, which was different from idiopathic OA and post-traumatic OA. Therefore, we need to use other types of OA models (idiopathic OA or a surgically induced OA model) to further verify its effect, and the side effects of chloramphenicol also need to be considered, such as myelosuppression.
Chloramphenicol reduced the severity of cartilage degradation in a type II collagen-induced rabbit model of OA, which may be related to induction of autophagy and inhibition of MMP-13 and IL-6.