Investigation into the anti‐inflammatory properties of metformin in intervertebral disc cells

INTRODUCTION: Intervertebral disc degeneration (IDD) is closely related to heightened inflammation in the annulus fibrosis (AF) and nucleus pulposus (NP) cells in the intervertebral disc. An imbalanced matrix homeostasis has been shown to contribute to disc degeneration and associated discogenic low back pain. Metformin, a diabetes medication, has been noted to exhibit anti‐inflammatory properties through upregulation of the AMPK pathway, leading to various anti‐inflammatory‐related responses in hepatocytes. However, it is still unclear how metformin influences disc cellular response to inflammatory stress and the corresponding mechanism. Hence, the objective of this study is to elucidate the effects of metformin on expression of key pro‐inflammatory, catabolic, and anabolic factors within rat AF cells in response to inflammatory stimulation and mechanical tensile stress. METHODS: Five Fischer 344 rats were sacrificed and their spines isolated. AF cells were cultured and plated in flexible silicone membrane‐based six‐well plates. Wells were split into eight groups and subjected to metformin, IL‐1β, mechanical stretch, and combined treatments. Relative gene expressions of MMP‐13, COX‐2, iNOS, AGC, and Col1 were assessed with quantitative real‐time polymerase chain reaction (qRT‐PCR), and downstream prostaglandin E(2) (PGE2) production was quantified with enzyme‐linked immunosorbent assay (ELISA). NF‐kB nuclear translocation was also quantified. RESULTS: Metformin in the presence of the combined stress treatments (M + IL/S) significantly increased Col1, COX‐2, and MMP‐13 gene expression, decreased PGE2 production compared to IL/S conditions alone. Metformin treatment of cultured rat annulus fibrosus cells significantly reduced the nuclear translocation of NF‐κB after 4 h of IL‐1β treatment from 43.1% in case of IL‐1β treatment down to 26.2% in the case of metformin + IL‐1β treatment. DISCUSSION: The lack of metformin‐mediated suppression of inflammatory response in the nonstretch groups indicates that metformin may be enacting its effects through a stretch‐dependent manner. These results suggest a foundation for pursuing further research into metformin's potential role as an anti‐inflammatory agent for curtailing intervertebral disc degeneration.