From King's Lab, Shanghai Jiao Tong University School of Pharmacy, Shanghai, China.
Anesthesiology. 2014 Apr;120(4):962-75. doi: 10.1097/ALN.0b013e3182a66d2a.
D-Amino acid oxidase (DAAO) is a flavin adenine dinucleotide-dependent peroxisomal flavoenzyme which is almost exclusively expressed within astrocytes in the spinal cord. DAAO catalyzes oxidation of D-amino acids to hydrogen peroxide, which is a stable and less active reactive oxygen species, and may represent a final form of reactive oxygen species. This study tested the hypothesis that the spinal astroglial DAAO-hydrogen peroxide pathway plays an important role in the development of morphine antinociceptive tolerance.
Rat and mouse formalin, hot-plate, and tail-flick tests were used, and spinal DAAO expression and hydrogen peroxide level were measured. Sample size of animals was six in each study group.
Subcutaneous and intrathecal DAAO inhibitors, including 5-chloro-benzo[d]isoxazol-3-ol, AS057278, and sodium benzoate, completely prevented and reversed morphine antinociceptive tolerance in the formalin, hot-plate, and tail-immersion tests, with a positive correlation to their DAAO inhibitory activities. Intrathecal gene silencers, small interfering RNA/DAAO and small hairpin RNA/DAAO, almost completely prevented morphine tolerance. Intrathecal 5-chloro-benzo[d]isoxazol-3-ol and small interfering RNA/DAAO completely prevented increased spinal hydrogen peroxide levels after chronic morphine treatment. Intrathecal nonselective hydrogen peroxide scavenger phenyl-tert-N-butyl nitrone and the specific hydrogen peroxide catalyst catalase also abolished established morphine tolerance. Spinal dorsal horn astrocytes specifically expressed DAAO was significantly up-regulated, accompanying astrocyte hypertrophy after chronic morphine treatment.
For the first time, the authors' result identify a novel spinal astroglial DAAO-hydrogen peroxide pathway that is critically involved in the initiation and maintenance of morphine antinociceptive tolerance, and suggest that this pathway is of potential utility for the management of morphine tolerance and chronic pain.
D-氨基酸氧化酶（DAAO）是一种黄素腺嘌呤二核苷酸依赖性过氧化物酶体黄素酶，几乎仅在脊髓中的星形胶质细胞中表达。DAAO 催化 D-氨基酸氧化为过氧化氢，过氧化氢是一种稳定且活性较低的活性氧物种，可能代表活性氧物种的最终形式。本研究检验了这样一个假设，即脊髓星形胶质细胞 DAAO-过氧化氢途径在吗啡镇痛耐受的发展中起着重要作用。
使用大鼠和小鼠福尔马林、热板和尾巴闪烁试验，并测量脊髓 DAAO 表达和过氧化氢水平。每组研究动物的样本量为六只。
皮下和鞘内 DAAO 抑制剂，包括 5-氯苯并[d]异恶唑-3-醇、AS057278 和苯甲酸钠，完全预防和逆转了福尔马林、热板和尾巴浸泡试验中的吗啡镇痛耐受，与它们的 DAAO 抑制活性呈正相关。鞘内基因沉默剂，小干扰 RNA/DAAO 和短发夹 RNA/DAAO，几乎完全预防了吗啡耐受。鞘内 5-氯苯并[d]异恶唑-3-醇和小干扰 RNA/DAAO 完全阻止了慢性吗啡处理后脊髓过氧化氢水平的升高。鞘内非选择性过氧化氢清除剂苯基叔丁基硝酮和特异性过氧化氢催化剂过氧化氢酶也消除了已建立的吗啡耐受。脊髓背角星形胶质细胞特异性表达 DAAO 显著上调，伴随慢性吗啡处理后星形胶质细胞肥大。
作者的研究结果首次确定了一种新的脊髓星形胶质细胞 DAAO-过氧化氢途径，该途径对于吗啡镇痛耐受的起始和维持至关重要，并表明该途径对于吗啡耐受和慢性疼痛的管理具有潜在的应用价值。
