Protective effects of alpinetin against interleukin-1β-exposed nucleus pulposus cells: Involvement of the TLR4/MyD88 pathway in a cellular model of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) causes a variety of symptoms such as low back pain, disc herniation, and spinal stenosis, which can lead to high social and economic costs. Alpinetin has an anti-inflammatory potential, but its effect on IDD is unclear. Herein, we investigated the effect of alpinetin on IDD. To mimic an in vitro model of IDD, nucleus pulposus cells (NPCs) were exposed to interleukin 1β (IL-1β). The viability of NPCs was assessed by CCK-8 assay. The expression of Toll-like receptor 4 (TLR4), myeloid differentiation primary response protein 88 (MyD88), aggrecan, collagen-2, and matrix metalloproteinase-3 (MMP-3) was examined by qRT-PCR and western blotting. The protein levels of B cell lymphoma-2 (Bcl-2), Bcl-2-associated protein X (Bax), and cleaved caspase-3 were scrutinized by western blotting. The flow cytometry assay was performed to assess apoptosis of NPCs. The contents of inflammatory factors were examined by ELISA kits. Results showed that alpinetin repressed IL-1β-tempted activation of the TLR4/MyD88 pathway and apoptosis in NPCs. Alpinetin alleviated IL-1β-tempted inflammatory responses and oxidative stress in NPCs. Moreover, alpinetin lessened IL-1β-tempted extracellular matrix (ECM) degeneration in NPCs by enhancing the expression of aggrecan and collagen-2 and reducing the expression of MMP-3. The effects of alpinetin on IL-1β-exposed NPCs were neutralized by TLR4 upregulation. In conclusion, alpinetin repressed IL-1β-tempted apoptosis, inflammatory responses, oxidative stress, and ECM degradation in NPCs through the inactivation of the TLR4/MyD88 pathway.