Fucoidan attenuates the existing allodynia and hyperalgesia in a rat model of neuropathic pain

Fucoidan is an active constituent found in brown seaweeds, which have potential neuroprotection. The current study aimed to investigate the effects of fucoidan on the maintenance of neuropathic pain induced by L5 spinal nerve ligation (SNL) and the underlying mechanism related to the spinal neuroimmune responses. Animals were randomized into 5 groups: sham-operation with vehicle and SNL with vehicle or fucoidan (15, 50, and 100 mg/kg). Different doses of fucoidan or vehicle were administered intrathecally once daily from postoperative day (POD) 11-20. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) was measured on 1 day before operation and days 10, 20, 22, 24, 26, 28, 30 after operation. Glial activation markers such as glial fibrillary acidic protein (GFAP) and macrophage antigen complex-1 (mac-1), inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 activation, and extracellular signalregulated protein kinase (ERK) activation in the lumbar spinal cord were determined on day 30 after operation. The results showed that fucoidan caused dose-dependently attenuation of mechanical allodynia and thermal hyperalgesia. Furthermore, fucoidan could markedly inhibit neuroimmune activation characterized by glial activation, production of cytokines as well as ERK activation. The analgesic effect of intrathecal fucoidan in rats receiving SNL might partly attribute to the inhibition of neuroimmune activation associated with the maintenance of neuropathic pain.