Kimura T, Ho I K, Yamamoto I
Department of Hygienic Chemistry, Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi, Kanazawa, Japan.
Sleep. 2001 May 1;24(3):251-60. doi: 10.1093/sleep/24.3.251.
This review deals with the concept of sleep mechanism based on our uridine receptor theory. It is well established that uridine is one of the sleep-promoting substances, we have, therefore, synthesized new types of hypnotic compounds from oxopyrimidine nucleosides. Their mechanism of action in CNS depressant effects is elucidated based on the receptor theory. In this study, structure-activity relationship for CNS depressant properties, sleep-promoting effects, interaction with certain CNS receptors, and receptor binding assay of uridine derivatives as oxopyrimidine nucleoside were investigated. In the studies of structure-activity relationship of N3-substituted uridine, we found for the first time that both N3-benzyluridine and N3-phenacyluridine synthesized exhibited potent hypnotic activity (loss of righting reflex) by intracerebroventicular injection in mice. Moreover, certain derivatives of these compounds possessed synergistic effects with barbiturate and benzodiazepine, and decreased in spontaneous activity, motor incoordination, and antianxiety effects in mice. Especially, N3-phenacyluridine markedly enhanced pentobarbital- and diazepam-induced sleep by 6- and 70-fold, respectively. However, N3-benzyluracil and N3-phenacyluracil that have no ribose moiety did not possess any hypnotic activity, indicating specific effects of nucleoside derivatives. Effects of N3-benzyluridine on natural sleep in rats were thus examined. N3-Benzyluridine also possessed the sleep promoting effect assessed by electrocorticogram at the dose of 10 pmol. For elucidating the mechanism of action of N3-phenacyluridine, the interactions of this compound with benzodiazepine, GABA, 5-HT, or adenosine receptors were also investigated. Although the pharmacological activity of N3-phenacyluridine was high, the affinities to benzodiazepine, GABA, 5-HT, and adenosine receptors were quite low. [3H]N3-Phenacyluridine concentration-dependently bound to synaptic membrane prepared from the bovine brain. The Scatchard analysis revealed a single component of the binding site. This binding site is proposed here as a novel receptor called "uridine receptor" for hypnotic activity of the uridine derivatives. The rank order of the distribution of these specific binding sites was found to be striatum > thalamus > cerebral cortex > cerebellum > mid brain > medulla oblongata in the rat brain. In the metabolic study of N3-phenacyluridine, we found that this compound was exclusively metabolized to N3-(S)-(+)-alpha-hydroxy-beta-phenethyluridine, but not the (R)- form, in mice. N3-(S)-(+)-alpha-Hydroxy-beta-phenylethyluridine possessed not only strong hypnotic activity but also a high affinity to the uridine receptor of synaptic membranes, while the (R)-isomer was low in both activities. Racemic mixture was shown to be intermediate for pharmacological effects of the compounds. These studies which used (R)- or (S)-isomer indicate that uridine binding site or uridine receptor, exists in the CNS and plays some role in sleep regulation in mammals as one of the triggering steps in inducing hypnotic activity. It is suggested that uridine is released from steps of nucleic acid-nucleic protein biosynthesis (catabolism), and reaches the binding sites in the areas of the brain which regulate natural sleep. The uridine dissociated from the receptor is then utilized for the synthesis of nucleic acid (anabolism). We propose here that the induction of sleep may be mediated by uridine through uridine receptor in the CNS, although the structure of uridine receptor is not yet elucidated.
本综述基于我们的尿苷受体理论探讨睡眠机制的概念。尿苷是公认的促睡眠物质之一，因此我们从氧嘧啶核苷合成了新型催眠化合物。基于受体理论阐明了它们在中枢神经系统抑制作用中的作用机制。在本研究中，我们研究了尿苷衍生物作为氧嘧啶核苷的中枢神经系统抑制特性、促睡眠作用、与某些中枢神经系统受体的相互作用以及受体结合测定的构效关系。在N3-取代尿苷的构效关系研究中，我们首次发现，通过向小鼠脑室内注射合成的N3-苄基尿苷和N3-苯甲酰甲基尿苷均表现出强效催眠活性（翻正反射消失）。此外，这些化合物的某些衍生物与巴比妥类和苯二氮䓬类具有协同作用，并可降低小鼠的自发活动、运动不协调和抗焦虑作用。特别是，N3-苯甲酰甲基尿苷分别使戊巴比妥和地西泮诱导的睡眠显著增强了6倍和70倍。然而，没有核糖部分的N3-苄基尿嘧啶和N3-苯甲酰甲基尿嘧啶不具有任何催眠活性，表明核苷衍生物具有特异性作用。因此，我们研究了N3-苄基尿苷对大鼠自然睡眠的影响。N3-苄基尿苷在剂量为10 pmol时也具有通过脑电图评估的促睡眠作用。为了阐明N3-苯甲酰甲基尿苷的作用机制，我们还研究了该化合物与苯二氮䓬、GABA、5-羟色胺或腺苷受体的相互作用。虽然N3-苯甲酰甲基尿苷的药理活性很高，但它与苯二氮䓬、GABA、5-羟色胺和腺苷受体的亲和力相当低。[3H]N3-苯甲酰甲基尿苷浓度依赖性地与从牛脑制备的突触膜结合。Scatchard分析显示结合位点为单一成分。本文提出这个结合位点是一种新型受体，称为“尿苷受体”，它参与尿苷衍生物的催眠活性。在大鼠脑中，这些特异性结合位点的分布顺序为纹状体>丘脑>大脑皮层>小脑>中脑>延髓。在N3-苯甲酰甲基尿苷的代谢研究中，我们发现该化合物在小鼠体内仅代谢为N3-(S)-(+)-α-羟基-β-苯乙基尿苷，而不是(R)-异构体。N3-(S)-(+)-α-羟基-β-苯乙基尿苷不仅具有很强的催眠活性，而且对突触膜的尿苷受体具有高亲和力，而(R)-异构体在这两种活性方面都很低。外消旋混合物显示为这些化合物药理作用的中间值。这些使用(R)-或(S)-异构体的研究表明，尿苷结合位点或尿苷受体存在于中枢神经系统中，并且在哺乳动物的睡眠调节中作为诱导催眠活性的触发步骤之一发挥一定作用。提示尿苷从核酸-核酸蛋白生物合成（分解代谢）步骤中释放出来，并到达调节自然睡眠的脑区中的结合位点。然后从受体解离的尿苷被用于核酸（合成代谢）合成。我们在此提出，睡眠的诱导可能是由尿苷通过中枢神经系统中的尿苷受体介导的，尽管尿苷受体的结构尚未阐明。
