BACKGROUND

Neuropathic pain is a complex state of chronic pain that is usually accompanied by peripheral and central nervous system damage or dysfunction. Previous studies have indicated that neuroinflammation in the spinal cord is an important contributor to neuropathological and behavioral abnormalities. A series of early inflammatory markers, such as IL-1, TNF-α, and IFN-γ, and advanced inflammatory markers, such as high-mobility group box 1 (HMGB1), are involved in neuroinflammation.

STUDY DESIGN

A randomized, double blind, controlled animal trial.

OBJECTIVE

In this study, a lentivirus delivering human IL-10 (LV/hIL-10) was administered intrathecally to determine the effects of IL-10 on allodynia and hyperalgesia in a chronic constriction injury-induced (CCI) rat model of neuropathic pain.

METHODS

Sprague-Dawley rats weighting 260 - 320 g were randomly divided into 4 groups. Group Sham (Sham), Group CCI±Normal Saline (NS), Group CCI±LV/hIL-10 (LV/hIL-10), and Group CCI±LV/control (vector). Rats in each group were intrathecally delivered with NS, LV/control, or recombinant vector LV/hIL-10 in a total volume of 10 μl. Paw withdrawal mechanical thresholds (PWMT) and paw withdrawal thermal latency PWTL were measured one day before CCI (baseline) and 0, 3, 7, 14, and 28 days after intrathecal administration. Cerebrospinal fluid (CSF) samples were collected during surgical plane anesthesia and the collected CSF samples were used to assay for human IL-10, rat IL-1β, rat IL-6, and rat TNF-α by enzyme-linked immunosorbent assay (ELISA). Animals were sacrificed and the L4-5 lumbar segment of the spinal cord was removed for determination of green fluorescent protein (GFP) expression. Immunohistochemical analysis was performed using anti HMGB1 antibodies and the expression of HMGB1 protein in the spinal cord was determined by western blot analysis after intrathecal delivery (n = 8 each).

RESULTS

The results show that intrathecal LV/hIL-10 reverses enhanced pain states. Moreover, the increased level of HMGB1 exhibited in a late stage of CCI was inhibited by exogenous overexpression of hIL-10 in the CCI model. Expression of HMGB1, RAGE, and pAkt were lower in CCI-induced rats treated with LV/hIL-10 than in those treated with LV/control (vector) or saline (NS). Our results showed that IL-10 inhibits activation of the inflammatory HMGB1-RAGE pathway in the CCI rat model.

LIMITATIONS

Further experimental investigations are needed to clarify the specific biological roles played by HMGB1 in IL-10-mediated regulation of neuropathic pain.

CONCLUSION

Our results indicate that intrathecal lentiviral-mediated transfer of IL-10 attenuates CCI-induced neuropathic pain in rats. The anti-thermal hyperalgesia and anti-mechanical allodynia may be partly attributable to the decreased expression of HMGB1 and inhibition of HMGB1-RAGE pathway.