Thiamine, pyridoxine, cyanocobalamin and their combination inhibit thermal, but not mechanical hyperalgesia in rats with primary sensory neuron injury.

Neuropathic pain after nerve injury is severe and intractable, and current drugs and nondrug therapies offer substantial pain relief to no more than half of affected patients. The present study investigated the analgesic roles of the B vitamins thiamine (B1), pyridoxine (B6) and cyanocobalamin (B12) in rats with neuropathic pain caused by spinal ganglia compression (CCD) or loose ligation of the sciatic nerve (CCI). Thermal hyperalgesia was determined by a significantly shortened latency of foot withdrawal to radiant heat, and mechanical hyperalgesia was determined by a significantly decreased threshold of foot withdrawal to von Frey filaments stimulation of the plantar surface of hindpaw. Results showed that (1) intraperitoneal injection of B1 (5, 10, 33 and 100 mg/kg), B6 (33 and 100 mg/kg) or B12 (0.5 and 2 mg/kg) significantly reduced thermal hyperalgesia; (2) the combination of B1, B6 and B12 synergistically inhibited thermal hyperalgesia; (3) repetitive administration of vitamin B complex (containing B1/B6/B12 33/33/0.5 mg/kg, for 1 and 2 wk) produced long-term inhibition of thermal hyperalgesia; and (4) B vitamins did not affect mechanical hyperalgesia or normal pain sensation, and exhibited similar effects on CCD and CCI induced-hyperalgesia. The present studies demonstrate effects of B vitamins on pain and hyperalgesia following primary sensory neurons injury, and suggest the possible clinical utility of B vitamins in the treatment of neuropathic painful conditions following injury, inflammation, degeneration or other disorders in the nervous systems in human beings.