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. Endothelium-derived nitric oxide (NO)2 is a potent vasodilator that plays a critical role in maintaining vascular homeostasis through its antiatherogenic and antiproliferative effects on the vascular wall. Altered NO biosynthesis has been implicated in the pathogenesis of cardiovascular disease, and evidence from animal models and clinical studies suggests that accumulation of the endogenous nitric-oxide synthase (NOS) inhibitors, asymmetric dimethylarginine (ADMA) and N Gmethyl-L-arginine (L-NMMA) contribute to reduced NO generation and disease pathogenesis (1, 2). ADMA and L-NMMA are derived from the proteolysis of methylated arginine residues on various proteins. The methylation is carried out by a group of enzymes referred to as protein-arginine methyltransferases (3). Protein arginine methylation has been identified as an important post-translational modification involved in the regulation of DNA transcription, protein function, and cell signaling (4, 5). Upon proteolysis of methylated proteins, free methylarginines are released and can function as competitive inhibitors of NOS activity. The intracellular levels of these free methylarginines are regulated through the...

Dimethylarginine Dimethylaminohydrolase 2 Gene Polymorphism and Its Association with Asymmetrical Dimethyl Arginine in Hemodialyzed Patients

“…Investigations of ADMA concentration by independent methods in patients with renal failure, have identified plasma ADMA concentration as a strong independent predictor of disease progression. Of particular interest was the finding that a 0.1 µmol/L increase in plasma ADMA was associated with a 20% increase in cardiovascular event rate [7,33].…”

“…Several groups have demonstrated that modulating DDAH activity can have a profound effect on endothelial NO production [7,36,37]. Two isoforms of DDAH have been identified.…”

“…One of the main effects of oxidative stress is the decrease in the biological activity of NO [28]. Among the mechanisms for impaired NO synthesis is the accumulation of the endogenous NOS inhibitor asymmetric ADMA [7]. ADMA inhibits all three isoforms of nitric oxide synthase and therefore has the potential to produce diverse biological effects, particularly in the cardiovascular system [26,30].…”

“…Evidences from both animal models and clinical studies suggests that accumulation of the endogenous nitric-oxide synthase (NOS) inhibitors, ADMA and NGmethyl-L-arginine (L-NMMA) contributes to reducing nitric oxide (NO) [6,7].…”

146 Demethylation Treatment Restores Erectile Function in a Rat Model of Hyperhomocysteinemia

“…41,42 Additionally, Pope et al concluded that DDAH-mediated endothelium function "is largely ADMA-dependent and latter ADMA-independent." 43 On the other hand, since ADMA is taken up by endothelium, ADMA could accumulate and metabolize by DDAH intracellularly. 44 Hcy is a metabolic byproduct forming during the methionine cycle.…”