Accumulation of methylglyoxal increases the advanced glycation end-product levels in DRG and contributes to lumbar disk herniation-induced persistent pain.

Lumbar disk herniation (LDH) with discogenic low back pain and sciatica is a common and complicated musculoskeletal disorder. The underlying mechanisms are poorly understood, and there are no effective therapies for LDH-induced pain. In the present study, we found that the patients who suffered from LDH-induced pain had elevated plasma methylglyoxal (MG) levels. In rats, implantation of autologous nucleus pulposus (NP) to the left lumbar 5 spinal nerve root, which mimicked LDH, induced mechanical allodynia, increased MG level in plasma and dorsal root ganglion (DRG), and enhanced the excitability of small DRG neurons (<30 µm in diameter). Intrathecal injection of MG also induced mechanical allodynia, and its application to DRG neurons ex vivo increased the number of action potentials evoked by depolarizing current pulses. Furthermore, inhibition of MG accumulation by aminoguanidine attenuated the enhanced excitability of small DRG neurons and the mechanical allodynia induced by NP implantation. In addition, NP implantation increased levels of advanced glycation end products (AGEs) in DRG, and intrathecal injection of MG-derived AGEs induced the mechanical allodynia and DRG neuronal hyperactivity. Intrathecal injection of MG also significantly increased the expression of AGEs in DRG. Importantly, scavenging of MG by aminoguanidine also attenuated the increase in AGEs induced by NP implantation. These results suggested that LDH-induced MG accumulation contributed to persistent pain by increasing AGE levels. Thus generation of AGEs from MG may represent a target for treatment of LDH-induced pain.NEW & NOTEWORTHY Our study demonstrates that methylglyoxal accumulation via increasing advanced glycation end-product levels in dorsal root ganglion contributes to the persistent pain induced by lumbar disk herniation, which proposed potential targets for the treatment of lumbar disk herniation-induced persistent pain.

Activation of the RAGE/STAT3 Pathway in the Dorsal Root Ganglion Contributes to the Persistent Pain Hypersensitivity Induced by Lumbar Disc Herniation.

BACKGROUND: Clinically, chronic low back pain and sciatica associated with lumbar disc herniation (LDH) is a common musculoskeletal disorder. Due to the unawareness of detailed mechanisms, it is difficult to get an effective therapy. OBJECTIVE: The aim of the present study was to identify the role of the RAGE/STAT3 pathway in the dorsal root ganglion (DRG) on the formation and development of persistent pain hypersensitivity induced by LDH. STUDY DESIGN: Controlled animal study. SETTING: University laboratory. METHODS: After LDH induced by implantation of autologous nucleus pulposus (NP, harvested from animal tail) on the left L5 nerve root was established, mechanical thresholds and electrophysiological tests were conducted at relevant time points during an observation period of 28 days. Protein levels and localization of RAGE and p-STAT3 were performed by using Western blotting and immunohistochemistry, respectively. RESULTS: LDH induced persistent pain hypersensitivity, increased excitability of DRG neurons, and upregulated the expression of RAGE and p-STAT3 in the DRG. Consecutive injection of both RAGE antagonist FPS-ZM1 (i.t.) and STAT3 activity inhibitor S3I-201 (i.t.) inhibited the enhanced excitability of DRG neurons and mechanical allodynia induced by NP implantation. Furthermore, local knockdown of STAT3 by intrathecal injection of AAV-Cre-GFP into STAT3flox/flox mice markedly alleviated NP implantation-induced mechanical allodynia in mice. Importantly, the expression of p-STAT3 was colocalized with that of RAGE in the DRG and inhibition of RAGE with FPS-ZM1 prevented NP implantation-induced STAT3 activation. LIMITATIONS: More underlying mechanism(s) of the role of the RAGE/STAT3 pathway on the formation and development of persistent pain hypersensitivity induced by LDH will be needed to be explored in future research. CONCLUSIONS: These findings suggest activation of the RAGE/STAT3 pathway plays a critical role in persistent pain induced by LDH, and this pathway may represent novel therapeutic targets for the treatment of LDH-induced persistent pain. KEY WORDS: Lumbar disc herniation, persistent pain, RAGE, STAT3, DRG.