Introduction:

Adiponectin, a hormone secreted by adipocytes, is known to have anti-inflammatory and insulin resistance effects. Previous reports have shown that adiponectin decreased TNF-α expression in nucleus pulposus (NP) cells, and TNF-α was a pivotal contributor to Intervertebral disc (IVD) degeneration contributed to low back pain. The purpose of this study is to investigate the therapeutic value and the molecular mechanism of AdipoRon, an orally active adiponectin receptor agonist, on IVD degeneration through an in vitro study using a three-dimensional cell culture device and an in vivo study using a rat tail puncture model.

METHODS:

In vitro: Eighteen human NP cells were obtained from consented patients (nine males and nine females, mean age: 47.1 year-old) during surgical procedures for lumbar degenerative disc disease. NP cells were pre-cultured in a Tapered Stencil for Cluster Culture device for three-dimensional cell culture. After pre-culture, these cells were assigned to the following four groups: Group C; cells cultured without treatment, Group A; cells cultured with AdipoRon treatment, Group I; cells cultured with IL-1β treatment, Group A+I; cells cultured with both AdipoRon and IL-1β treatment. Extracellular matrix (ECM) metabolism, proinflammatory cytokines, and inflammation pathway levels were assessed by western blotting in each Group.

In vivo: We established a model of IVD degeneration by needle puncture of rat tail and compared the disc height and histology across the following three groups. Group C; the control group, Group P; rats with needle puncture only, Group P+A; rats with AdipoRon injection after the puncture. IVD height on X-ray was expressed as disc height index (%DHI). Histological analysis of IVD was performed according to the histological degeneration scale.

RESULTS:

In vitro: Western blotting results showed that expression levels of proinflammatory cytokines (TNF-α and IL-6) and ECM catabolic factors (MMP-13 and ADAMTS-4) were significantly upregulated by IL-1β treatment (p<0.01). Moreover, Group A+I showed significantly decreased expression levels compared to Group I (p<0.01). In the AMPK pathway, Group A and A+I showed increased expression of p-AMPK compared to Group I (p<0.01), and Group A+I showed decreased expression of p-NFkB compared to Group I (p<0.01).

In vivo findings: Group P showed a significant decrease in %DHI upon measurement at 14 and 28 days post puncture compared to group C (p<0.01). Group P+A showed a significantly smaller decrease in %DHI compared to group P (p<0.01). Histological analysis showed a significant degenerative change of IVD in Group P and P+A compared with Group C at 14 and 28 days post puncture (p<0.01). However, Group P+A showed significant suppression of the progression of IVD degeneration compared with Group P.

DISCUSSION:

This study demonstrated that the AdipoRon treatment resulted in decreased proinflammatory cytokines and ECM catabolic factors in human NP cells via the AMPK pathway. Additionally, the treatment with AdipoRon prevented the IVD degeneration in the rat IVD degeneration model. Our results suggest that AdipoRon might potentially lead to the reduction of IVD degeneration and might even LBP.