King's Lab, School of Pharmacy, Shanghai Jiao Tong University, Shanghai, 200240, China.
Amino Acids. 2012 Nov;43(5):1905-18. doi: 10.1007/s00726-012-1390-z. Epub 2012 Sep 21.
D-Amino acid oxidase (DAAO), a FAD-dependent peroxisomal flavoenzyme that catalyzes oxidation of D-amino acids to hydrogen peroxide, is distributed in the spinal cord almost exclusively expressed within astrocytes. The present study aims to explore potential contributions of spinal DAAO to the development of bone cancer pain and morphine tolerance to analgesia. Tibia inoculation of carcinoma cells produced mechanical allodynia (but not heat hyperalgesia), in synchronous with induction of DAAO expression and DAAO enzymatic activity, as well as activation of spinal astrocytes marked by GFAP. Subcutaneous and intrathecal injection of the specific DAAO inhibitor CBIO (5-chloro-benzo[d]isoxazol-3-ol) blocked mechanical allodynia in a dose- and time-dependent manner in tumor-bearing rats, with maximum inhibition of 40-50 %. Multi-daily intrathecal injections of the DAAO gene silencer siRNA/DAAO also yielded anti-allodynic effects by approximately 40 % and the analgesia remained for at least 6 days. Subcutaneous injection of CBIO suppressed the production of spinal hydrogen peroxide and GFAP expression. 7-Day multiple bi-daily injections of CBIO produced anti-allodynia without inducing self-tolerance to analgesia or cross-tolerance to morphine, and concurrent injections of CBIO with morphine produced apparent additive anti-allodynia and completely prevented morphine tolerance in behaviors and spinal expression of μ-opioid receptors. Our results provide the first evidence that spinal DAAO contributes to the development of morphine tolerance to analgesia and bone cancer pain accounting for 40-50 % pain status, probably via production of hydrogen peroxide leading to activation of astrocytes. The unique characterizations of DAAO inhibitors make them a potential for the treatment of cancer pain when they are administered alone or in combination with morphine.
D-氨基酸氧化酶（DAAO）是一种 FAD 依赖性过氧化物酶体黄素酶，可催化 D-氨基酸氧化为过氧化氢，主要分布于脊髓，几乎仅在星形胶质细胞中表达。本研究旨在探讨脊髓 DAAO 对骨癌痛的发展和吗啡镇痛耐受的潜在贡献。癌细胞胫骨接种可产生机械性痛觉过敏（但不产生热痛觉过敏），同时诱导 DAAO 表达和 DAAO 酶活性以及星形胶质细胞激活，以 GFAP 为标志。特异性 DAAO 抑制剂 CBIO（5-氯苯并[d]异恶唑-3-醇）的皮下和鞘内注射以剂量和时间依赖的方式阻断荷瘤大鼠的机械性痛觉过敏，最大抑制率为 40-50%。多日鞘内注射 DAAO 基因沉默剂 siRNA/DAAO 也可产生约 40%的抗痛觉过敏作用，且镇痛作用至少持续 6 天。皮下注射 CBIO 可抑制脊髓过氧化氢和 GFAP 表达的产生。7 天多次双日皮下注射 CBIO 可产生抗痛觉过敏作用，而不会诱导镇痛耐受或对吗啡交叉耐受，同时注射 CBIO 和吗啡可产生明显的相加抗痛觉过敏作用，并完全防止吗啡在行为和脊髓 μ 阿片受体表达上的耐受。我们的研究结果首次证明，脊髓 DAAO 有助于吗啡镇痛耐受和骨癌痛的发展，占疼痛状态的 40-50%，可能是通过产生过氧化氢导致星形胶质细胞激活。DAAO 抑制剂的独特特性使其具有单独使用或与吗啡联合使用治疗癌症疼痛的潜力。
