Dayal Sanjana, Rodionov Roman N, Arning Erland, Bottiglieri Teodoro, Kimoto Masumi, Murry Daryl J, Cooke John P, Faraci Frank M, Lentz Steven R
Dept. of Internal Medicine, Univ. of Iowa, C32 GH, Iowa City, IA 52242, USA.
Am J Physiol Heart Circ Physiol. 2008 Aug;295(2):H816-25. doi: 10.1152/ajpheart.01348.2007. Epub 2008 Jun 20.
Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, has been proposed to be a mediator of vascular dysfunction during hyperhomocysteinemia. Levels of ADMA are regulated by dimethylarginine dimethylaminohydrolase (DDAH). Using both in vitro and in vivo approaches, we tested the hypothesis that hyperhomocysteinemia causes downregulation of the two genes encoding DDAH (Ddah1 and Ddah2). In the MS-1 murine endothelial cell line, the addition of homocysteine decreased NO production but did not elevate ADMA or alter levels of Ddah1 or Ddah2 mRNA. Mice heterozygous for cystathionine beta-synthase (Cbs) and their wild-type littermates were fed either a control diet or a high-methionine/low-folate (HM/LF) diet to produce varying degrees of hyperhomocysteinemia. Maximal relaxation of the carotid artery to the endothelium-dependent dilator acetylcholine was decreased by approximately 50% in Cbs(+/-) mice fed the HM/LF diet compared with Cbs(+/+) mice fed the control diet (P < 0.001). Compared with control mice, hyperhomocysteinemic mice had lower levels of Ddah1 mRNA in the liver (P < 0.001) and lower levels of Ddah2 mRNA in the liver, lung, and kidney (P < 0.05). Downregulation of DDAH expression in hyperhomocysteinemic mice did not result in an increase in plasma ADMA, possibly due to a large decrease in hepatic methylation capacity (S-adenosylmethionine-to-S-adenosylhomocysteine ratio). Our findings demonstrate that hyperhomocysteinemia causes tissue-specific decreases in DDAH expression without altering plasma ADMA levels in mice with endothelial dysfunction.
不对称二甲基精氨酸（ADMA）是一氧化氮（NO）合酶的内源性抑制剂，被认为是高同型半胱氨酸血症期间血管功能障碍的介质。ADMA的水平由二甲基精氨酸二甲氨基水解酶（DDAH）调节。我们采用体外和体内两种方法，检验了高同型半胱氨酸血症导致编码DDAH的两个基因（Ddah1和Ddah2）下调的假说。在MS-1小鼠内皮细胞系中，添加同型半胱氨酸可降低NO生成，但不会升高ADMA，也不会改变Ddah1或Ddah2 mRNA的水平。给胱硫醚β-合酶（Cbs）杂合小鼠及其野生型同窝小鼠喂食对照饮食或高蛋氨酸/低叶酸（HM/LF）饮食，以产生不同程度的高同型半胱氨酸血症。与喂食对照饮食的Cbs(+/+)小鼠相比，喂食HM/LF饮食的Cbs(+/-)小鼠的颈动脉对内皮依赖性舒张剂乙酰胆碱的最大舒张反应降低了约50%（P < 0.001）。与对照小鼠相比，高同型半胱氨酸血症小鼠肝脏中的Ddah1 mRNA水平较低（P < 0.001），肝脏、肺和肾脏中的Ddah2 mRNA水平较低（P < 0.05）。高同型半胱氨酸血症小鼠中DDAH表达的下调并未导致血浆ADMA升高，这可能是由于肝脏甲基化能力大幅下降（S-腺苷甲硫氨酸与S-腺苷同型半胱氨酸的比率）。我们的研究结果表明，高同型半胱氨酸血症会导致小鼠出现组织特异性的DDAH表达降低，而不会改变内皮功能障碍小鼠的血浆ADMA水平。
