Stress-induced signaling pathways in hyalin chondrocytes: inhibition by Avocado–Soybean Unsaponifiables (ASU)

SummaryObjectiveAvocado–Soybean Unsaponifiables (ASU) represent one of the most commonly used drugs for symptomatic osteoarthritis (OA). The mechanisms of its activities are still poorly understood. We investigate here the effects of ASU on signaling pathways in mouse or human chondrocytes.MethodsMouse or human chondrocytes stimulated with interleukin-1β (IL1β, 10ng/ml) and cartilage submitted to a compressive mechanical stress (MS) were studied in the presence or absence of ASU (10μg/ml). Nuclear factor κB (NF-κB) activation was assessed by immunoblot, using an I-κBα antibody, nuclear translocation of NF-κB using p65 antibody, and extra-cellular signal-regulated kinase (ERK)1/2 activation using phospho and ERK1/2 antibodies. The binding of the p50/p65 complex on DNA was studied by electrophoretic mobility shift assay.ResultsASU decrease matrix metalloproteinases-3 and -13 expressions and Prostaglandin E2 (PGE2) release in our model. The degradation of I-κBα is prevented in the presence of ASU as shown by the persistent expression of I-κBα protein in the cytosol when chondrocytes are stimulated by IL1β or MS. Nuclear translocation of the NF-κB complex is shown by the decrease of the p65 protein from the cytosol, whereas p65 appears in the nucleus under IL1β stimulation. This translocation is abolished in the presence of ASU. Moreover, bandshift experiments show an inhibition of the IL1β-induced binding of p50/p65 complexes to NF-κB responsive elements in response to ASU. Finally, among the different mitogen-activated protein kinases known to be induced by IL1β, ERK1/2 was the sole kinase inhibited by ASU.ConclusionThese results demonstrate that ASU express a unique range of activities, which could counteract deleterious processes involved in OA, such as inflammation