Enoxolone suppresses apoptosis in chondrocytes and progression of osteoarthritis via modulating the ERK1/2 signaling pathway
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Department of Orthopedics, Beijing Chaoyang Hospital, Capital Medical University, Beijing, China
Submission date: 2019-12-12
Final revision date: 2020-01-03
Acceptance date: 2020-01-04
Online publication date: 2020-02-24
Osteoarthritis (OA) is an inflammatory disorder of synovial joints which is mainly treated with therapeutic agents showing side effects associated with the gastrointestinal (GI) and metabolic system. Consequently, there is urgent need for a potent, safe and novel agent for treating OA and related disorders. Enoxolone is a pentacyclic triterpenoid obtained from the herb liquorice. Based on earlier findings, we postulated that enoxolone may produce chondroprotective activity by exerting anti-inflammatory, anti-catabolic and oxidative stress-decreasing effects.

Material and methods:
The chondrocytes were extracted from the femoral head articular cartilage of healthy rats. Immunofluorescence staining was done for identification of chondrocytes. Cell viability and proliferation studies were done using Cell Counting Kit-8. Apoptotic cells were identified by TUNEL assay and flow cytometry analysis. Autophagy was assessed by monodansylcadaverine assay. Western blot analysis was done for expression of proteins.

In the present study we investigated the protective effect of enoxolone on interleukin 1β (IL-1β) treated Iry chondrocytes in vitro. Treatment with IL-1β resulted in a significant reduction in cell viability of cells in increasing dose and time. Treatment with enoxolone along with IL-1β caused a significant decrease in growth inhibition. Also, enoxolone inhibited the IL-1β mediated apoptosis and activation of caspase-3 in cells. We also observed that enoxolone elevated the levels of p-ERK1/2, light chain 3 (LC3)-II and Beclin-1 (autophagy markers) in chondrocytes. The expression of (LC3)-II and Beclin-1 was decreased when the cells were treated with U0126 (ERK1/2 inhibitor).

Our findings demonstrate that enoxolone could suppress inflammatory signaling and apoptosis via the ERK1/2 pathway in chondrocytes.