title: Role of dimethylarginine dimethylaminohydrolases in the regulation of endothelial nitric oxide production.
abstract: Reduced NO is a hallmark of endothelial dysfunction, and among the mechanisms for impaired NO synthesis is the accumulation of the endogenous nitric-oxide synthase inhibitor asymmetric dimethylarginine (ADMA). Free ADMA is actively metabolized by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH), which catalyzes the conversion of ADMA to citrulline. Decreased DDAH expression/activity is evident in disease states associated with endothelial dysfunction and is believed to be the mechanism responsible for increased methylarginines and subsequent ADMA-mediated endothelial nitric-oxide synthase impairment. Two isoforms of DDAH have been identified; however, it is presently unclear which is responsible for endothelial ADMA metabolism and NO regulation. The current study investigated the effects of both DDAH-1 and DDAH-2 in the regulation of methylarginines and endothelial NO generation. Results demonstrated that overexpression of DDAH-1 and DDAH-2 increased endothelial NO by 24 and 18%, respectively. Moreover, small interfering RNA-mediated down-regulation of DDAH-1 and DDAH-2 reduced NO bioavailability by 27 and 57%, respectively. The reduction in NO production following DDAH-1 gene silencing was associated with a 48% reduction in l-Arg/ADMA and was partially restored with l-Arg supplementation. In contrast, l-Arg/ADMA was unchanged in the DDAH-2-silenced cells, and l-Arg supplementation had no effect on NO. These results clearly demonstrate that DDAH-1 and DDAH-2 manifest their effects through different mechanisms, the former of which is largely ADMA-dependent and the latter ADMA-independent. Overall, the present study demonstrates an important regulatory role for DDAH in the maintenance of endothelial function and identifies this pathway as a potential target for treating diseases associated with decreased NO bioavailability.
authors.affiliation: Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida 32607, USA.
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Pope
authors.forename: Kanchana
authors.initials: K
authors.lastname: Karrupiah
authors.forename: Patrick N
authors.initials: PN
authors.lastname: Kearns
authors.forename: Yong
authors.initials: Y
authors.lastname: Xia
authors.forename: Arturo J
authors.initials: AJ
authors.lastname: Cardounel
mesh_terms: D000581:Amidohydrolases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D002956:Citrulline / Q000096:biosynthesis* / Q000235:genetics; D004730:Endothelium, Vascular / Q000201:enzymology*; D015870:Gene Expression; D007527:Isoenzymes / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; C487735:dimethylarginine; D002956:Citrulline; D009569:Nitric Oxide; D001120:Arginine; D052250:Nitric Oxide Synthase Type III; D000581:Amidohydrolases; C059999:dimethylargininase