Changes in expression of Toll-like receptor 4 and its downstream cytokines in spinal cord in a rat model of bone cancer pain

Abstract

Objective To investigate the changes in the expression of Toll-like receptor 4(TLR4)and its downstream cytokines TNF-α and IL-1β in the spinal cord in a rat model of bone cancer pain.Methods Seventy-two female SD rats weighing 150-180 g were randomly divided into 3 groups(n = 24 each): group Ⅰ normal control(group C);group Ⅱ sham operation(group S)and group Ⅲ bone cancer pain(group BP).Bone cancer was induced by intra-tibial inoculation of 1× 10~5 Walker 256 breast cancer cells.Bone cancer and bone destruction were shown by X-ray.Paw withdrawal threshold (PWT) to mechanical stimulation was measured with von Frey filaments and spontaneous pain was evaluated by ambulatory score.The expression of TLR4,TNF-α and IL-1βmRNA in the spinal cord was determined by RT-PCR and the expression of TLR4 protein by immuno-histochemistry and TLR4 positive cell count was determined.Results In group BP the ambulatory score started increasing and PWT to mechanical stimulation started decreasing at 6 days after inoculation.The ambulatory score was significantly higher,PWT significantly lower and the expression of TLR4 mRNA and protein and TNF-α and IL-1β mRNA in the spinal cord and TLR4 positive cell count were significantly higher in group BP than in group C and S.Conclusion Intra-tibial inoculation of Walker 256 breast cancer cells activates TLR4 in the spinal cord,leading to the increased release of its downstream cytokines and mechanical hyperalgesia.TLR4 might be a potential target for the treatment of bone cancer pain. Key words: Bone neoplasms; Pain; Toll-like receptor 4; Tumor necrosis factor-alpha; Interleukin-1beta