脊髓D-氨基酸氧化酶为疼痛治疗新靶点的实验研究

D-型氨基酸氧化酶（D-amino acid oxidase，DAO）是一种以FAD的过氧化物酶体酶，催化D-丝氨酸等D-氨基酸生成相应的α-酮酸、NH3和H2O2．表达于多种组织。最近研究提示脊髓DAO可能与疼痛调节有关。我们采用DAO基因缺陷（ddY／DAO^-）小鼠和DAO选择性抑制剂苯甲酸钠在小鼠热水甩尾实验、热板实验、福尔马林实验和扭体实验中，观察DAO在急、慢性疼痛中的作用，     

柱前手性衍生化-HPLC法测定人血浆和尿液中D-谷氨酸和D-丝氨酸的浓度

目的:建立手性分离D-谷氨酸和D-丝氨酸的方法,测定人血浆和尿液中D-谷氨酸和D-丝氨酸的浓度。方法:12对极性氨基酸标准液混合后,加入衍生化试剂邻苯二甲醛、N-乙酰-L-半胱氨酸衍生化后,采用高效液相色谱法进样测定。色谱柱为大连依利特HypersilC18,流动相为甲醇-50mmol·L-1醋酸铵缓冲液(pH6.0),梯度洗脱,流速为1.0mL·min-1,柱温为室温,进样量为20μL,荧光检测波长为350nm(激发波长)、450nm(发射波长)。结果:D-谷氨酸、D-丝氨酸检测浓度分别在0.5～20、0.5～80nmol·L-1范围内线性关系良好,平均方法回收率分别为96.4%～103.6%、97.1%～100.5%,日内、日间RSD均<8%。测得正常人血浆中D-谷氨酸和D-丝氨酸平均含量分别为(2.43±0.37)、(1.07±0.11)nmol·mL-1,尿样中未能检测到2种D型氨基酸。结论:本研究建立的手性分离测定D-谷氨酸和D-丝氨酸的分析方法可行,可用于测定人血浆和尿液中二者的浓度。     

腹腔注射L-丝氨酸后大鼠梗死侧脑皮质L-丝氨酸与D-丝氨酸含量的测定

目的:制作大鼠永久性脑梗死模型,腹腔注射L-丝氨酸,测定梗死侧大脑皮质L-丝氨酸与D-丝氨酸含量的变化,为应用L-丝氨酸辅助治疗脑梗死提供方法学上的依据。方法:利用邻苯二甲醛及N-乙酰半胱氨酸柱前衍生,高效液相色谱荧光检测法测定脑组织中L-丝氨酸与D-丝氨酸含量。结果:流动相A为82%0.1 mol·L-1磷酸盐缓冲液,流动相B为18%甲醇条件下,L-丝氨酸与D-丝氨酸得到很好的分离;腹腔注射L-丝氨酸1 h后,梗死侧脑皮质L-丝氨酸含量迅速增加,2 h即达高峰[(6.85±0.30)μmol·g-1],为正常脑组织的4倍以上,12 h时仍是正常的2倍以上水平[(3.56±0.22)vs(1.52±0.04)μmol·g-1];D-丝氨酸水平升高缓慢,升高幅度低,6 h时达高峰,为正常的2倍多[(0.75±0.05)vs(0.32±0.01)μmol·g-1]。结论:腹腔注射L-丝氨酸能快速升高梗死侧大脑皮质L-丝氨酸水平,对D-丝氨酸影响相对较小。     

胰岛素降低海马谷氨酸和D-丝氨酸含量改善糖尿病大鼠空间学习记忆能力

目的观察胰岛素对糖尿病(DM)大鼠空间学习记忆及海马组织中谷氨酸和D-丝氨酸含量的影响。方法采用尾静脉注射链脲佐菌素(STZ)制备大鼠DM模型。注射STZ第3天建模成功后,大鼠sc给予胰岛素2 U·kg-1,每天1次,持续82 d。定期检测各组大鼠体质量及空腹血糖。第81天进行Morris水迷宫实验,检测大鼠学习记忆能力;实验结束后取海马组织,观察形态变化,并测定谷氨酸和D-丝氨酸含量。结果与正常对照组比较,DM模型组大鼠体质量明显减轻(P<0.01),血糖明显升高(P<0.01),逃避潜伏期明显延长,原平台象限游泳时间显著减少(P<0.01),海马组织中谷氨酸及D-丝氨酸的含量均显著升高(P<0.01)。胰岛素治疗组体质量增加,血糖含量恢复到正常水平。与DM模型组相比,胰岛素治疗组大鼠逃避潜伏期显著缩短(P<0.01),原平台象限游泳时间占总时间百分比显著增加(P<0.01);海马组织中谷氨酸和D-丝氨酸的含量也分别由DM模型组的(1.550±0.054)和(0.084±0.05)mg·g-1下降为胰岛素治疗组的(1.137±0.023)和(0.068±0.004)mg·g-1。结论胰岛素可以改善糖尿病大鼠空间学习记忆能力,这可能与其降低海马组织中谷氨酸和D-丝氨酸含量有关。     

D-丝氨酸在中枢神经系统的作用研究进展

长期以来,人们普遍认为D型氨基酸在高等生物中没有功能。但最近10年的研究表明,D丝氨酸不但能够被胶质细胞合成和分泌,而且能够作为共激活因子,作用于NMDA受体的“甘氨酸位点”,参与该受体的激活。该文对D丝氨酸在中枢神经系统的产生、代谢和作用进行了简要介绍。     

骨髓间充质干细胞对D-半乳糖衰老模型小鼠的实验研究

目的：研究骨髓间充质干细胞是否具有抗衰老作用。方法：采用5％D-半乳糖（0．25ml／10g）连续8周皮下注射建立衰老小鼠模型,并于模型建成后给予骨髓间充质干细胞输注。检测间充质干细胞治疗前后衰老相关指标：小鼠体重,免疫器官重量,肝组织、血清SOD活力和MDA含量,全血GSH—Px活力的变化,全面考察骨髓间充质干细胞的抗衰老作用。结果：骨髓间充质干细胞能对抗D-半乳糖所致小鼠肝组织和血清中MDA含量的升高,提高肝和血清SOD、全血GSH—Px的活力,并对抗小鼠体重、胸腺及脾脏指数下降。结论：骨髓间充质干细胞能改善D-半乳糖衰老模型小鼠的衰老相关指标,提示具有抗衰老作用。     

D-半乳糖衰老模型观察的新指标

目的观察D-半乳糖衰老模型与正常小鼠之间衰老指标的差别.方法采用D-半乳糖sc造成衰老小鼠模型,测定脑组织Ca2 含量、Ca2 -ATP酶(钙泵)、Na -ATP酶(钠泵)、NO和AngⅡ胰岛素(ISN)活性.结果D-半乳糖衰老模型小鼠与对照组比较脑组织Ca2 含量(P＜0.01)、NO水平(P＜0.05)明显增加;Ca2 -ATP酶、Na -ATP酶活性下降(P＜0.01),胰岛素、AngⅡ水平明显下降(P＜0.01),Zn2 /Cu2 比值有显著性差异.结论D-半乳糖衰老模型小鼠与正常小鼠之间在组织Ca2 含量、Ca2 -ATP酶(钙泵)、Na -ATP酶(钠泵)、NO、AngⅡ和胰岛素活性有显著性差异,Zn2 /Cu2 比值下降,可作为抗衰老药物研究的模型.     

蒺藜皂苷对D-半乳糖衰老模型小鼠的作用

目的：研究蒺藜皂苷对肛半乳糖所致小鼠学习记忆能力下降和各项衰老指标的对抗作用，以期探讨蒺藜皂苷的抗衰老作用机制。方法：以肛半乳糖衰老模型小鼠为实验对象，以其体质量、免疫器官质量，肝脑丙二醛（MDA）和脂褐素（LF）的含量，全血谷胱苷肽过氧化氢酶（GSH-Px）、红细胞过氧化氢酶（CAT）和脑中超氧化物歧化酶（SOD）的活力为指标，全面考察蒺藜皂苷的抗衰老作用。结果：蒺藜皂苷（50，100mg·kg^-1，ig），能对抗连续6周给肛半乳糖[5％，0．25mL·（10g）^-1]所致小鼠脑组织中LPO、LF含量的升高，提高全血GSH—Px．、红细胞CAT和脑中SOD的活力，并对抗小鼠体质量、脾脏及胸腺指数下降。结论：蒺藜皂苷能有效地对抗D-半乳糖所致的小鼠多项衰老指标的出现，促进衰老小鼠的学习记忆能力。     

DHA型磷脂酰丝氨酸对东莨菪碱痴呆模型小鼠学习记忆力的影响

目的 研究富含DHA的磷脂酰丝氨酸（DHA-PS）对老年痴呆小鼠学习记忆的影响。方法 通过对小鼠腹腔注射东莨菪碱建模,并进行行为学测试和测定小鼠海马组织中的乙酰胆碱（Ach）、乙酰胆碱酯酶（AchE）和超氧化物歧化酶（SOD）的活力。实验分组为：正常对照组（N）、模型组（AD）、多奈哌齐阳性对照组（P）、DHA-PS组和DHA与磷脂酰丝氨酸（PS）的混合物组（DHA+PS）。 结果 富含DHA的磷脂酰丝氨酸（DHA-PS）能降低水迷宫潜伏期,提高穿越平台次数和目标象限停留时间,能明显抑制AchE的活力和提高SOD的活力,而DHA+PS组效果比较差。结论 富含DHA的磷脂酰丝氨酸（DHA-PS）通过影响中枢胆碱能神经系统和脑内抗氧化系统,改善了东莨菪碱所致痴呆小鼠学习记忆能力且与其分子形式有关。     

D-青霉胺和二巯丙磺酸钠对汞致大鼠肾毒性的影响

目的　研究预投D- 青霉胺 (D- penicillamine ,DPA)和二巯丙磺酸钠 (2 ,3 - Dimercato 1 Propanesulfonate ,DMPS)对汞致急性肾毒性的保护作用及其机制。方法　 48只Wistar大鼠随机分成 6组。第 1组以 5mL/kg体重皮下注射质量分数为 0 . 9%的氯化钠溶液 ,第 2、3和 4组分别皮下注射 0 .75、1.5和 2 .5mg kgHgCl2 溶液。第 5、6组大鼠分别腹腔注射2 0 0 μmoLDMPS和 2 0 0 μmoLDPA ,2h后再投与 2 5mg/kgHgCl2 溶液。染毒 12h后 ,收集 12h尿样 ,测定尿N- 乙酰 - β- D- 氨基葡萄糖苷酶 (NAG)和尿碱性磷酸酶 (ALP)活力、尿蛋白和尿汞含量。染毒 48h后 ,切取肾脏和肝脏 ,分别测定肾脏和肝脏中的丙二醛 (MDA)和谷胱甘肽 (GSH)含量、谷胱甘肽过氧化物酶 (GSH- Px)活力、肝脏汞和肾脏汞含量。结果　DMPS显著降低NAG和ALP活力和尿蛋白含量 ;DPA明显降低NAG活力和尿蛋白含量 ,对ALP没有影响。DMPS显著降低肾脏MDA含量 ,而DPA对肾脏MDA含量没有影响。DMPS-和DPA两干预组在肾脏中GSH含量和GSH -Px活力都明显高于 2 . 5mg kg染汞组 ,差异有显著性。DPA能显著降低肾脏汞含量。结论　DMPS比DPA更能有效地保护肾功能。DMPS会显著减轻汞在肾脏的氧化损伤 ,而DPA则没有影响。DMPS和DPA能明显减少肾脏GSH和GSH- Px的耗     

Long-term treatment with morphine increases the D-serine content in the rat brain by regulating the mRNA and protein expressions of serine racemase and D-amino acid oxidase

Recent studies indicate that an endogenous co-agonist for an N-methyl-D-aspartate (NMDA) receptor-related glycine site, D-serine, is synthesized by serine racemase and is metabolized by D-amino acid oxidase (DAO) and that acute treatment with morphine augments the gene expression of serine racemase and DAO in rat brain. To further elucidate the mechanism underlying the activation of NMDA receptors following chronic opioid administration, we have evaluated the effects of the chronic administration of morphine on the mRNA and protein expressions of serine racemase and DAO and on the contents of D-serine in several areas of the rat brain. Repeated administration of morphine for 30 days produced a significant augmentation of both the mRNA and protein expressions of serine racemase in all the brain regions, whereas no significant change in the protein expression of DAO was observed in all the brain regions. Furthermore, the chronic administration caused a slight but significant elevation in the concentration of D-serine in the cortex, striatum, and hippocampus. These results indicate the elevated D-serine level following the chronic morphine treatment could at least in part be involved in the activation of NMDA receptors via the glycine site.     

Contributions of the D-serine pathway to schizophrenia

The glutamate neurotransmitter system is one of the major candidate pathways for the pathophysiology of schizophrenia, and increased understanding of the pharmacology, molecular biology and biochemistry of this system may lead to novel treatments. Glutamatergic hypofunction, particularly at the NMDA receptor, has been hypothesized to underlie many of the symptoms of schizophrenia, including psychosis, negative symptoms and cognitive impairment. This review will focus on D-serine, a co-agonist at the NMDA receptor that in combination with glutamate, is required for full activation of this ion channel receptor. Evidence implicating D-serine, NMDA receptors and related molecules, such as D-amino acid oxidase (DAO), G72 and serine racemase (SRR), in the etiology or pathophysiology of schizophrenia is discussed, including knowledge gained from mouse models with altered D-serine pathway genes and from preliminary clinical trials with D-serine itself or compounds modulating the D-serine pathway. Abnormalities in D-serine availability may underlie glutamatergic dysfunction in schizophrenia, and the development of new treatments acting through the D-serine pathway may significantly improve outcomes for many schizophrenia patients.     

Effects of MK-801 on the expression of serine racemase and d-amino acid oxidase mRNAs and on the D-serine levels in rat brain

We have investigated the acute effects of the increasing doses of non-competitive N-methyl-d-aspartate receptor antagonist MK-801 (0.2-1.6 mg/kg) on the expression of serine racemase and d-amino acid oxidase (DAO) mRNAs in several brain areas of rats. We have also evaluated the effects of the chronic administration of MK-801 (0.4 mg/kg) on the gene expression of serine racemase and DAO and on the d-serine concentrations. A dose-dependent augmentation of the expression of serine racemase mRNA was seen in most brain areas at both 1 and 4 h after the administration. In contrast, a drastic decline in the expression of DAO mRNA was observed in most brain areas 1 h after the MK-801 administration, whereas a dose-dependent elevation in the expression of DAO mRNA was observed in most brain areas 4 h after the administration. The chronic MK-801 administration produced a significant increase in the expression of serine racemase mRNA in almost all brain areas, whereas no significant changes were found in the level of DAO mRNA in most brain areas. In addition, the chronic administration caused a slight but significant elevation in the concentrations of d-serine in the cortex and striatum. These present findings indicate that increasing the serine racemase mRNA and no changes in the DAO mRNA after the chronic administration could contribute to the elevation of the d-serine level in the forebrain, and that serine racemase and DAO could play an important role in the regulation of N-methyl-d-aspartate receptors via the d-serine metabolism.     

Endogenous D-serine in mammalian brains]

It is well established that, like glycine and D-alanine, D-serine potentiates glutamate neurotransmission via the N-methyl-D-aspartate (NMDA) receptor by selective stimulation of its strychnine-insensitive glycine site and acts as a co-agonist of the glutamate receptor. D-Serine has been found to modify behavioral changes associated with higher brain functions such as memory, convulsion, anxiety, psychotomimetic-induced abnormal behavior and cerebellar ataxia. Interestingly, a substantial amount of free D-serine has been demonstrated in mammalian brains, although it has long been presumed that D-amino acids are uncommon in mammals. Free D-serine is predominantly concentrated in the brain with a persistent high content throughout life. The patterns of the regional variations and the postnatal changes in brain D-serine are closely correlated with those of the R2B subunit of the N-methyl-D-aspartate (NMDA) type excitatory amino acid receptor. Moreover, D-serine is released to the extracellular space and taken up into the brain homogenates, C6 glioma cells and primary culture of astrocytes of the rat cerebral cortex. Recently, the conversion of L-serine to its D-form by serine racemase has been suggested by in vivo and in vitro experiments. These data are consistent with the view that D-serine might be an intrinsic positive modulator of the brain NMDA receptor containing the R2B subunit and play a pivotal role in controlling behavioral expression in mammals.     

Effect of aminooxyacetic acid on extracellular level of D-serine in rat striatum: an in vivo microdialysis study

To elucidate the effect of an inhibitor of pyridoxal phosphate-dependent enzymes, aminooxyacetic acid, on the activity of serine racemase in vivo, we have investigated the effect of aminooxyacetic acid on the extracellular concentration of D-serine in the rat striatum using an in vivo microdialysis technique. The intrastriatal perfusion of aminooxyacetic acid caused a significant decline in the extracellular concentration of D-serine. These data, together with the fact that serine racemase is a pyridoxal phosphate-dependent enzyme, suggest that the aminooxyacetic acid-induced reduction of the extracellular D-serine may be at least in part due to the drug's ability to inhibit serine racemase.     

吗啡依赖小鼠脑组织cGMP水平、鸟苷酸环化酶及磷酸二酯酶活性的调节

以递增剂量吗啡sc,使小鼠产生对吗啡的躯体依赖,观察脑组织cGMP水平、PDE和sGC的活性变化及PKA对其磷酸化调节。结果表明,(1)小脑、纹状体、海马及大脑皮质cGMP含量显著降低;(2)在小脑、海马中sGC活性明显降低,PDE活性无明显变化,在纹状体及大脑皮质中均明显升高,且体外磷酸化水平也均明显下降,PKA抑制剂可抑制此变化;(3)纳洛酮拮抗组未见上述变化。结果提示,吗啡依赖小鼠脑组织cGMP水平普遍降低,在小脑和海马可能因sGC活性下降引起,在纹状体及大脑皮质可能因PDE活性升高所致。     

Effect of systemic administration of D-serine on the levels of D- and L-serine in several brain areas and periphery of rat

To obtain further insight into the distribution and metabolism of exogenous D-serine, we have investigated the effect of the intraperitoneal administration of D-serine (10 mmol/kg) on the concentrations of D- and L-serine in several brain areas and periphery of infant and adult rats. The administration produced a significant augmentation of the D-serine levels not only in the cortex but also in the hippocampus, striatum, cerebellum and periphery. The rapid decline in the enhanced D-serine levels was observed in the periphery and cerebellum, whereas the injection caused a prolonged elevation of the D-serine levels in the cortex and hippocampus. The application caused a slight increase in the L-serine levels in several brain areas and periphery 3 or 6 h after the injection, whereas a significant decrease in the L-serine concentration was observed in the periphery, diencephalon and cerebellum 3 or 7 days after the injection. Because a structural abnormality and N-methyl-D-aspartate (NMDA) receptor hypofunction has been demonstrated in the cortex and hippocampus of schizophrenic subjects, D-serine treatment may offer a new therapeutic approach to diseases related to the hypofunction of NMDA receptors such as schizophrenia.     

Blood D-Amino Acid Oxidase Levels Increased With Cognitive Decline Among People With Mild Cognitive Impairment: A Two-Year Prospective Study

BackgroundDysregulation of N-methyl-D-aspartate receptor (NMDAR) neurotransmission has been reported to be implicated in the pathogenesis of Alzheimer’s disease (AD). D-amino acid oxidase (DAO), responsible for degradation of NMDAR-related D-amino acids such as D-serine, regulates NMDAR function. A cross-section study found that serum DAO levels were positively related with the severity of cognitive aging among elderly individuals. This 2-year prospective study aimed to explore the role of DAO levels in predicting the outcome of patients with very early-phase AD, such as mild cognitive impairment (MCI).MethodsFifty-one patients with MCI and 21 healthy individuals were recruited. Serum DAO levels and cognitive function, measured by the AD assessment scale-cognitive subscale and the Mini-Mental Status Examination, were monitored every 6 months. We employed multiple regressions to examine the role of DAO concentration in cognitive decline in the 2-year period.ResultsFrom baseline to endpoint (24 months), serum DAO levels increased significantly, and cognitive ability declined according to both cognitive tests in the MCI patients. Among the healthy individuals, DAO concentrations also increased and Mini-Mental Status Examination scores declined; however, AD assessment scale-cognitive subscale scores did not significantly change. Further, DAO levels at both months 12 and 18 were predictive of cognitive impairment at month 24 among the MCI patients.ConclusionsTo our knowledge, this is the first study to demonstrate that blood DAO levels increased with cognitive deterioration among the MCI patients in a prospective manner. If replicated by future studies, blood DAO concentration may be regarded as a biomarker for monitoring cognitive change in the patients with MCI.     

Physiological function and metabolism of free D-alanine in aquatic animals

Aquatic crustaceans and some bivalve mollusks contain a large amount of free D-alanine (up to 100 mumol/g wet wt.) in their tissues. Under high salinity stress, crustaceans and bivalve mollusks largely accumulate D- and L-alanine irrespective of species examined, together with L-glutamine, L-proline, and glycine of which increases are species dependent. These data indicate that D-alanine is one of the major compatible osmolytes responsible for the intracellular isosmotic regulation in the tissues of crustaceans and bivalves. Alanine racemase has been proven to catalyze the interconversion of D- and L-alanine in these invertebrates. The enzyme has been isolated to homogeneity from the muscle of black tiger prawn Penaeus monodon and its cDNA has been cloned from the muscle and hepatopancreas of kuruma prawn Penaeus japonicus for the first time in eukaryotes other than yeast. Several fish species fed on crustaceans and mollusks contain D-amino acid and D-aspartate oxidases that catalyze the decomposition of D-amino acids. A cDNA of D-amino acid oxidase has been cloned from the hepatopancreas of omnivorous common carp Cyprinus carpio. During oral administration of free D-alanine to carp, the activity and mRNA of D-amino acid oxidase increased rapidly in hepatopancreas and the increases were highest in intestine followed by hepatopancreas and kidney. These data suggest that D-amino acid oxidase is inducible in carp and an important enzyme responsible for the efficient utilization of carbon skeleton of D-alanine in their feeds.