Institute of Toxicology, Core Unit Proteomics, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625, Hannover, Germany.
Amino Acids. 2019 Mar;51(3):483-494. doi: 10.1007/s00726-018-2684-6. Epub 2018 Dec 8.
Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are endogenous inhibitors of nitric oxide (NO) synthase. SDMA is excreted in the urine without major metabolization. About 10% of daily produced ADMA are excreted unchanged in the urine. The major elimination route of ADMA (about 90%) involves its hydrolysis to dimethylamine (DMA) and L-citrulline by dimethylarginine dimethylaminohydrolase (DDAH) and excretion of DMA in the urine. High circulating and low excretory concentrations of ADMA are considered risk factors. Experimentally, DDAH activity can be inhibited by SH-specific agents such as inorganic and organic mercury compounds, and by S-nitrosothiols which block the SH group of a particular cysteine moiety of DDAH that is essential for its hydrolytic activity. Alternatively, DDAH activity can be inhibited by organic compounds that compete with the substrate ADMA for DDAH. Arginine analogs that contain substituents on guanidine nitrogen atom(s) (N) represent a class of DDAH inhibitors. In the present study, we investigated the effects of physiological and natural amino acid derivatives of L-arginine and L-citrulline as well as of nitrate and nitrite, the major circulating and excretory metabolites of NO and NO donating drugs. Here, we report for the first time that the physiological N-hydroxy-L-arginine, an isolable intermediate in NO synthesis, inhibits recombinant DDAH-1 activity (IC ≈ 100 µM). Two plant L-citrulline derivatives, i.e., N,N-dimethyl-L-citrulline and N,N-dimethyl-N-hydroxy-L-citrulline (connatin), were found to inhibit almost completely hepatic DDAH activity in vitro in rat homogenate at a concentration of 100 µM each. At pharmacological concentrations (i.e., 1 mM), inorganic nitrate, but not inorganic nitrite, was found to increase rat liver DDAH activity. In urine of 18 patients with Becker's muscular dystrophy, nitrate was found to correlate closely with DMA (Spearman, r = 0.73, p = 0.002). In summary, N-hydroxy-L-arginine, N,N-dimethyl-L-citrulline and N,N-dimethyl-N-hydroxy-L-citrulline are novel inhibitors of DDAH activity. This article provides an overview of amino acid-based DDAH inhibitors and discusses potential underlying inhibition mechanisms.
不对称二甲基精氨酸（ADMA）和对称二甲基精氨酸（SDMA）是一氧化氮（NO）合酶的内源性抑制剂。SDMA 未经主要代谢即排泄于尿液中。约 10%的每日产生的 ADMA 以未改变的形式排泄于尿液中。ADMA 的主要消除途径（约 90%）涉及 ADMA 被二甲基精氨酸二甲氨基水解酶（DDAH）水解为二甲胺（DMA）和 L-瓜氨酸，然后将 DMA 排泄于尿液中。高循环和低排泄浓度的 ADMA 被认为是危险因素。实验中，DDAH 活性可被 SH 特异性试剂如无机和有机汞化合物抑制，也可被 S-亚硝基硫醇抑制，后者阻断 DDAH 中特定半胱氨酸部分的 SH 基团，而该基团对于其水解活性是必需的。或者，DDAH 活性可被与 ADMA 竞争 DDAH 的有机化合物抑制。胍基氮原子（N）上有取代基的精氨酸类似物代表一类 DDAH 抑制剂。在本研究中，我们研究了 L-精氨酸和 L-瓜氨酸以及硝酸盐和亚硝酸盐的生理和天然氨基酸衍生物作为 NO 和 NO 供体药物的主要循环和排泄代谢物对 DDAH 活性的影响。在此，我们首次报道生理 N-羟-L-精氨酸，NO 合成中的一种可分离的中间产物，可抑制重组 DDAH-1 活性（IC≈100µM）。两种植物 L-瓜氨酸衍生物，即 N,N-二甲基-L-瓜氨酸和 N,N-二甲基-N-羟-L-瓜氨酸（康纳丁），在大鼠肝匀浆中，在 100µM 浓度下，被发现几乎完全抑制 DDAH 活性。在药理学浓度（即 1mM）下，无机硝酸盐而非亚硝酸盐被发现可增加大鼠肝 DDAH 活性。在 18 名贝克氏肌营养不良症患者的尿液中，发现硝酸盐与 DMA 密切相关（Spearman，r=0.73，p=0.002）。总之，N-羟-L-精氨酸、N,N-二甲基-L-瓜氨酸和 N,N-二甲基-N-羟-L-瓜氨酸是 DDAH 活性的新型抑制剂。本文概述了基于氨基酸的 DDAH 抑制剂，并讨论了潜在的抑制机制。
