King's Laboratory, School of Pharmacy, Shanghai Jiao Tong University, Shanghai, China.
J Pharmacol Exp Ther. 2010 Jan;332(1):248-54. doi: 10.1124/jpet.109.158816. Epub 2009 Oct 14.
D-amino acid oxidase (DAO) is an enzyme catalyzing oxidative deamination of neutral and polar d-amino acids and is expressed in the kidneys, liver, and central nervous system (CNS) including the spinal cord. We have previously demonstrated that DAO gene deletion/mutation by using mutant ddY/DAO(-/-) mice and systemic administration of the DAO inhibitor sodium benzoate blocked formalin-induced hyperalgesia in mice. In this study, we further investigated the potential role of DAO in neuropathic pain in a rat model of tight L(5)/L(6) spinal nerve ligation. After L(5)/L(6) spinal nerve ligation, the mRNA expression (measured by real-time quantitative polymerase chain reaction) and enzyme activity (measured by a colorimetric method) of DAO in the lumbar spinal cord were markedly increased, in agreement with the development of neuropathic pain (mechanical allodynia). Intraperitoneal injection of sodium benzoate (400 mg/kg) specifically blocked mechanical allodynia in neuropathic rats and formalin-induced hyperalgesia but did not suppress acute pain responses in the tail-flick test or formalin test. Systemic injection of sodium benzoate also inhibited DAO activity in the lumbar spinal cord of rats. Furthermore, direct intrathecal (spinal cord) injection of benzoate (30 mug/rat) specifically blocked spinal nerve ligation-induced mechanical allodynia in neuropathic rats and formalin-induced hyperalgesia (but not acute pain) in the formalin test. Based on the above results, we conclude that spinal DAO plays a pronociceptive (rather than an antinociceptive) role and might be a target molecule for the treatment of chronic pain of neuropathic origin.
D-氨基酸氧化酶（DAO）是一种催化中性和极性 D-氨基酸氧化脱氨的酶，在肾脏、肝脏和中枢神经系统（CNS）中表达，包括脊髓。我们之前已经证明，使用突变 ddY/DAO(-/-) 小鼠和系统给予 DAO 抑制剂苯甲酸钠可以消除 DAO 基因缺失/突变，从而阻断小鼠福尔马林诱导的痛觉过敏。在这项研究中，我们进一步研究了 DAO 在紧密结扎 L(5)/L(6) 脊神经的大鼠模型中对神经病理性疼痛的潜在作用。在 L(5)/L(6) 脊神经结扎后，腰椎脊髓中 DAO 的 mRNA 表达（通过实时定量聚合酶链反应测量）和酶活性（通过比色法测量）显著增加，与神经病理性疼痛（机械性痛觉过敏）的发展一致。腹腔内注射苯甲酸钠（400mg/kg）特异性阻断神经病理性大鼠的机械性痛觉过敏和福尔马林诱导的痛觉过敏，但不抑制尾部闪烁试验或福尔马林试验中的急性疼痛反应。全身注射苯甲酸钠也抑制了大鼠腰椎脊髓中的 DAO 活性。此外，直接鞘内（脊髓）注射苯甲酸钠（30μg/只）特异性阻断神经结扎诱导的机械性痛觉过敏和福尔马林诱导的痛觉过敏（但不引起急性疼痛）在福尔马林试验中。基于上述结果，我们得出结论，脊髓 DAO 发挥致痛作用（而不是镇痛作用），可能是治疗神经源性慢性疼痛的靶标分子。
