Effect of curcumin on expression of p-ERK and p-CREB in spinal dorsal horn and dorsal root ganglion in type 2 diabetic neuropathic pain in rats

Abstract

Objective To evaluate the effects of curcumin on the expression of phosphorylated extracellular signal-related kinase (p-ERK) and phosphorylated cAMP response element binding protein (p-CREB) in the spinal dorsal horn and dorsal root ganglion (DRG) in type 2 diabetic neuropathic pain (DNP) in rats.Methods Type 2 diabetes mellitus was induced by high-fat and high-sucrose diet and intraperitoneal streptozotocin (STZ) 35mg/kg,and confirmed by fasting blood glucose level≥ 16.7 mmol/L in male Sprague-Dawley rats.Type 2 DNP was confirmed by the mechanical withdrawal threshold (MWT) and thermal withdraw latency (TWL) measured on day 14 after STZ administration ＜ 80％ of the baseline value,and the rats with type 2 DNP were randomly divided into 3 groups (n =27 each):type 2 DNP group (group DNP),curcumin group (group Cur) and solvent control group (group SC).Curcumin and corn oil 100 mg/kg (25 mg/ml) were injected intraperitoneally once a day for 14consecutive days starting from 14 days after administration of streptozocin in Cur and SC groups,respectively.Another 27 normal rats were served as control group (group C) and were fed with common forage.MWT and TWL were measured at 3,7 and 14 days after curcumin injection (T1 3),and the lumbar segment 4-6 of the spinal cord and DRGs were removed at the same time for determination of the expression of p-ERK and p-CREB (by Western blot).Results Compared with group C,MWT was significantly decreased,TWL was shortened,and the expression of p-ERK and p-CREB in spinal dorsal horn and DRGs was up-regulated at T1-3 in DNP and SC groups,and at T1 in Cur group (P ＜ 0.05).Compared with group DNP,MWT was significantly increased,TWL was prolonged,and the expression of p-ERK and p-CREB in spinal dorsal horn and DRGs was down-regulated at T2,3 in Cur group (P ＜0.05).There was no significant difference in the MWT,TWL and expression of p-ERK and p-CREB between DNP and SC groups (P ＞ 0.05).Conclusion Curcumin can attenuate type 2 diabetic DNP by inhibiting up-regulation of the expression of p-ERK and p-CREB in the spinal dorsal horn and DRG in rats. Key words: Curcumin; Diabetes mellitus, type 2 ; Neuralgia; Spinal cord ; Ganglia, spinal; Extracellular signal-regulated MAP kinases; Cyclic AMP response element-binding protein