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[EXPRESS] TRPA1 sensitization during diabetic vascular impairment contributes to cold hypersensitivity in a mouse model of painful diabetic peripheral neuropathy.

Research paper by Haruka H Hiyama, Yuichi Y Yano, Kanako K So, Satoshi S Imai, Kazuki K Nagayasu, Hisashi H Shirakawa, Takayuki T Nakagawa, Shuji S Kaneko

Indexed on: 04 Jul '18Published on: 04 Jul '18Published in: Molecular Pain



Abstract

Diabetic peripheral neuropathy is a common long-term complication of diabetes. Accumulating evidence suggests that vascular impairment plays important roles in the pathogenesis of diabetic peripheral neuropathy, while the mechanism remains unclear. We recently reported that transient receptor potential ankyrin 1 (TRPA1) is sensitized by hypoxia, which can contribute to cold hypersensitivity. In this study, we investigated the involvement of TRPA1 and vascular impairment in painful diabetic peripheral neuropathy using streptozotocin-induced diabetic model mice. Streptozotocin-induced diabetic model mice showed mechanical and cold hypersensitivity with a peak at 2 weeks after the streptozotocin administration, which were likely to be paralleled with the decrease in the skin blood flow of the hindpaw. Streptozotocin-induced cold hypersensitivity was significantly inhibited by an antagonist HC-030031 (100 mg/kg) or deficiency for TRPA1, whereas mechanical hypersensitivity was unaltered. Consistent with these results, the nocifensive behaviors evoked by an intraplantar injection of the TRPA1 agonist allyl-isothiocyanate (AITC) were enhanced 2 weeks after the streptozotocin administration. Both streptozotocin-induced cold hypersensitivity and the enhanced AITC-evoked nocifensive behaviors were significantly inhibited by a vasodilator, tadalafil (10 mg/kg), with recovery of the decreased skin blood flow. Similarly, in a mouse model of hindlimb ischemia induced by the ligation of the external iliac artery, AITC-evoked nocifensive behaviors were significantly enhanced 3 and 7 days after the ischemic operation, whereas mechanical hypersensitivity was unaltered in TRPA1-knockout mice. However, no difference was observed between wildtype and TRPA1-knockout mice in the hyposensitivity for current or mechanical stimulation or the deceased density of intraepidermal nerve fibers 8 weeks after the streptozotocin administration. These results suggest that TRPA1 sensitization during diabetic vascular impairment causes cold, but not mechanical, hypersensitivity in the early painful phase of diabetic peripheral neuropathy. However, TRPA1 may play little or no role in the progression of diabetic peripheral neuropathy.