Active site mutant dimethylarginine dimethylaminohydrolase 1 expression confers an intermediate tumour phenotype in C6 gliomas.

Dimethylarginine dimethylaminohydrolase (DDAH) metabolizes the endogenous inhibitor of nitric oxide synthesis, asymmetric dimethylarginine (ADMA). Constitutive over-expression of DDAH1, the isoform primarily associated with neuronal nitric oxide synthase (nNOS) results in increased tumour growth and vascularization, and elevated VEGF secretion. To address whether DDAH1-mediated tumour growth is reliant upon the enzymatic activity of DDAH1, cell lines expressing an active site mutant of DDAH1 incapable of metabolizing ADMA were created. Xenografts derived from these cell lines grew significantly faster than those derived from control cells, yet not as fast as those over-expressing wild-type DDAH1. VEGF expression in DDAH1 mutant-expressing tumours did not differ from control tumours but was significantly lower than that of wild-type DDAH1-over-expressing tumours. Fluorescence microscopy for CD31 and pimonidazole adduct formation demonstrated that DDAH1 mutant-expressing tumours had a lower endothelial content and demonstrated less hypoxia, respectively, than wild-type DDAH1-expressing tumours. However, there was no difference in uptake of the perfusion marker Hoechst 33342. Non-invasive multiparametric quantitative MRI, including the measurement of native T(1) and T(2) relaxation times and apparent water diffusion coefficient, was indicative of higher cellularity in DDAH1-expressing xenografts, which was confirmed by histological quantification of necrosis. C6 xenografts expressing active site mutant DDAH1 displayed an intermediate phenotype between tumours over-expressing wild-type DDAH1 and control tumours. These data suggest that enhanced VEGF expression downstream of DDAH1 was dependent upon ADMA metabolism, but that the DDAH1-mediated increase in tumour growth was only partially dependent upon its enzymatic activity, and therefore must involve an as-yet unidentified mechanism. DDAH1 is an important mediator of tumour progression, but appears to have addition roles independent of its metabolism of ADMA, which need to be considered in therapeutic strategies targeted against the NO/DDAH pathway in cancer.

Circulating methylarginine levels and the decline in renal function in patients with chronic kidney disease are modulated by DDAH1 polymorphisms.

In patients with chronic kidney disease, high plasma levels of the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine, are thought to contribute to decline in renal function. Here we took a candidate gene approach to determine any causal role of asymmetric dimethylarginine in the progression of chronic kidney disease. The impact of single-nucleotide polymorphisms in the genes encoding the two isoforms of the asymmetric dimethylarginine-degrading enzyme, dimethylarginine dimethylaminohydrolase (DDAH1 and DDAH2), on enzyme expression, plasma asymmetric dimethylarginine levels, and longitudinal changes in estimated glomerular filtration rate were determined in various patient groups. There was evidence suggesting that the rs17384213 DDAH1 GG genotype was associated with increased expression of its mRNA in kidney allografts. Healthy subjects carrying the rs17384213 G allele had lower plasma asymmetric dimethylarginine, and a similar borderline association was found in patients with chronic kidney disease. This allele, however, was independently associated with a steeper decline in renal function in two separate cohorts of patients with chronic kidney disease. We conclude that polymorphisms in DDAH1 alter the rate of decline of glomerular filtration rate in subjects with chronic kidney disease. Our findings show that DDAH1 modulates plasma asymmetric dimethylarginine and contributes to the decline in renal function. However, it appears that increases in circulating methylarginine did not mediate progressive kidney injury.

Metabolomic profiling of amines in sepsis predicts changes in NOS canonical pathways.

RATIONALE: Nitric oxide synthase (NOS) is a biomarker/target in sepsis. NOS activity is driven by amino acids, which cycle to regulate the substrate L-arginine in parallel with cycles which regulate the endogenous inhibitors ADMA and L-NMMA. The relationship between amines and the consequence of plasma changes on iNOS activity in early sepsis is not known. OBJECTIVE: Our objective was to apply a metabolomics approach to determine the influence of sepsis on a full array of amines and what consequence these changes may have on predicted iNOS activity. METHODS AND MEASUREMENTS: 34 amino acids were measured using ultra purification mass spectrometry in the plasma of septic patients (n = 38) taken at the time of diagnosis and 24-72 hours post diagnosis and of healthy volunteers (n = 21). L-arginine and methylarginines were measured using liquid-chromatography mass spectrometry and ELISA. A top down approach was also taken to examine the most changed metabolic pathways by Ingenuity Pathway Analysis. The iNOS supporting capacity of plasma was determined using a mouse macrophage cell-based bioassay. MAIN RESULTS: Of all the amines measured 22, including L-arginine and ADMA, displayed significant differences in samples from patients with sepsis. The functional consequence of increased ADMA and decreased L-arginine in context of all cumulative metabolic changes in plasma resulted in reduced iNOS supporting activity associated with sepsis. CONCLUSIONS: In early sepsis profound changes in amine levels were defined by dominant changes in the iNOS canonical pathway resulting in functionally meaningful changes in the ability of plasma to regulate iNOS activity ex vivo.

all-trans-Retinoic acid increases nitric oxide synthesis by endothelial cells: a role for the induction of dimethylarginine dimethylaminohydrolase.

all-trans-Retinoic acid (atRA) has important effects on the developing and mature cardiovascular system. Nitric oxide (NO) production has been associated with the atRA-induced differentiation of neuronal cells, and we hypothesized that NO may also mediate certain actions of atRA in the cardiovascular system. We studied the effects of atRA on NO production by endothelial cells and determined whether regulation of enzymes responsible for metabolism of asymmetric dimethylarginine (ADMA) contributed to the effects seen. Murine endothelioma (sEnd.1) cells were incubated with or without atRA. Nitrite production was determined using the Griess reaction. The expression of NO synthase (NOS) and dimethylarginine dimethylaminohydrolase (DDAH) genes was determined by Northern blotting. A reporter gene assay was also used to study the effect of atRA on the DDAH II promoter. atRA significantly increased nitrite production by sEnd.1 cells despite no increase in eNOS expression. atRA also increased DDAH II gene expression and promoter activity and reduced the ratio of ADMA to symmetric dimethylarginine (SDMA) in culture medium. The DDAH inhibitor 4124W significantly reduced the induction of NO synthesis by atRA. The present study demonstrates that atRA increases NO synthesis in endothelial cells without increasing eNOS expression. atRA also increases the expression of DDAH II, the predominant DDAH isoform in endothelial cells. Our data suggests that the induction of NO synthesis by atRA may be facilitated by DDAH II. This pathway may help to explain some of the effects of atRA on the cardiovascular system.

Metabolism of asymmetric dimethylarginines is regulated in the lung developmentally and with pulmonary hypertension induced by hypobaric hypoxia.

BACKGROUND: Nitric oxide (NO) plays an important part in lowering pulmonary vascular resistance after birth, and in persistent pulmonary hypertension of the newborn (PPHN), NO-mediated dilation is dysfunctional. The endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) circulates in plasma, and its concentrations are elevated in certain cardiovascular diseases, including pulmonary hypertension. ADMA is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), the activity of which regulates ADMA concentrations and provides a mechanism for modulating NO synthase in vivo. We investigated the changes in expression and activity of the 2 isoforms of DDAH in lungs from newborn piglets both during normal development and in PPHN. METHODS AND RESULTS: Using Western blotting, we showed that DDAHI expression did not change in the normal developing lung; however, DDAHII increased after birth and reached a peak at 1 day. This was reflected in an increase in total DDAH activity according to an L-citrulline assay. With pulmonary hypertension, no changes in DDAHI expression were observed, but DDAHII expression was markedly decreased compared with age-matched controls. Total DDAH activity was similarly reduced. CONCLUSIONS: These results indicate that each DDAH isoform is differentially regulated during both lung development and PPHN. Suppression of DDAHII isoform expression may be a mechanism underlying PPHN.

Evidence for dysregulation of dimethylarginine dimethylaminohydrolase I in chronic hypoxia-induced pulmonary hypertension.

BACKGROUND: Chronic hypoxia-induced pulmonary hypertension is associated with increased pulmonary expression of nitric oxide synthase (NOS) enzymes. Nevertheless, some reports have indicated decreased pulmonary production of NO in the disease. To address this paradox, we determined pulmonary concentrations of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) in the hypoxia-induced pulmonary hypertension rat model. In addition, we determined whether dysregulation of the ADMA-metabolizing enzyme dimethylarginine dimethylaminohydrolase I (DDAH I) plays a role in this disease. METHODS AND RESULTS: Adult male rats were exposed for 1 week to either normoxia or hypoxia (10% oxygen). Lung tissues were used for Western blot analysis of endothelial NOS and DDAH I expression, measurement of lung NO and ADMA content, and in vitro assay of DDAH enzyme activity. Western blot analysis revealed a 1.9-fold increase in endothelial NOS protein and a 37% decrease in DDAH I protein in the lungs of hypoxia-exposed rats. Both pulmonary DDAH enzyme activity and NO content were significantly decreased in the hypoxic group (by 37% and 22%, respectively), but pulmonary ADMA concentrations were increased by 2.3-fold compared with the normoxic group. CONCLUSIONS: These data demonstrate that the rat chronic hypoxia-induced pulmonary hypertension model is associated with increased pulmonary concentrations of the NOS inhibitor ADMA. Moreover, pulmonary hypertensive rats exhibit reduced pulmonary expression and activity of the ADMA-metabolizing enzyme DDAH I. The decreased DDAH I and increased ADMA concentrations may therefore contribute to pulmonary hypertension via the competitive inhibition of pulmonary NOS enzymes.

Effects of ADMA upon gene expression: an insight into the pathophysiological significance of raised plasma ADMA.

BACKGROUND: Asymmetric dimethylarginine (ADMA) is a naturally occurring inhibitor of nitric oxide synthesis that accumulates in a wide range of diseases associated with endothelial dysfunction and enhanced atherosclerosis. Clinical studies implicate plasma ADMA as a major novel cardiovascular risk factor, but the mechanisms by which low concentrations of ADMA produce adverse effects on the cardiovascular system are unclear. METHODS AND FINDINGS: We treated human coronary artery endothelial cells with pathophysiological concentrations of ADMA and assessed the effects on gene expression using U133A GeneChips (Affymetrix). Changes in several genes, including bone morphogenetic protein 2 inducible kinase (BMP2K), SMA-related protein 5 (Smad5), bone morphogenetic protein receptor 1A, and protein arginine methyltransferase 3 (PRMT3; also known as HRMT1L3), were confirmed by Northern blotting, quantitative PCR, and in some instances Western blotting analysis to detect changes in protein expression. To determine whether these changes also occurred in vivo, tissue from gene deletion mice with raised ADMA levels was examined. More than 50 genes were significantly altered in endothelial cells after treatment with pathophysiological concentrations of ADMA (2 microM). We detected specific patterns of changes that identify pathways involved in processes relevant to cardiovascular risk and pulmonary hypertension. Changes in BMP2K and PRMT3 were confirmed at mRNA and protein levels, in vitro and in vivo. CONCLUSION: Pathophysiological concentrations of ADMA are sufficient to elicit significant changes in coronary artery endothelial cell gene expression. Changes in bone morphogenetic protein signalling, and in enzymes involved in arginine methylation, may be particularly relevant to understanding the pathophysiological significance of raised ADMA levels. This study identifies the mechanisms by which increased ADMA may contribute to common cardiovascular diseases and thereby indicates possible targets for therapies.

Selective substrate-based inhibitors of mammalian dimethylarginine dimethylaminohydrolase.

The enzyme DDAH metabolizes methylarginines that are inhibitors of nitric oxide synthase (NOS). Substrate-based inhibitors of mammalian DDAH have been synthesized, with optimization to give selective inhibition of DDAH with no significant direct effect on NOSs. These are the first examples of reversible DDAH inhibitors with significant activity and selectivity. In vivo administration increases plasma ADMA levels, giving proof of concept that these inhibitors can be used to probe the physiological effects of DDAH inhibition, with potential for pharmaceutical use of DDAH inhibitors in diseases where excess NO production is implicated.

Dimethylarginine dimethylaminohydrolase 1 is involved in spinal nociceptive plasticity.

Activation of neuronal nitric oxide synthase, and consequent production of nitric oxide (NO), contributes to spinal hyperexcitability and enhanced pain sensation. All NOS isoforms are inhibited endogenously by asymmetric dimethylarginine, which itself is metabolised by dimethylarginine dimethylaminohydrolase (DDAH). Inhibition of DDAH can indirectly attenuate NO production by elevating asymmetric dimethylarginine concentrations. Here, we show that the DDAH-1 isoform is constitutively active in the nervous system, specifically in the spinal dorsal horn. DDAH-1 was found to be expressed in sensory neurons within both the dorsal root ganglia and spinal dorsal horn; L-291 (NG-[2-Methoxyethyl]-L-arginine methyl ester), a DDAH-1 inhibitor, reduced NO synthesis in cultured dorsal root ganglia neurons. Spinal application of L-291 decreased N-methyl-D-aspartate-dependent postdischarge and windup of dorsal horn sensory neurons--2 measures of spinal hyperexcitability. Finally, spinal application of L-291 reduced both neuronal and behavioral measures of formalin-induced central sensitization. Thus, DDAH-1 may be a potential therapeutic target in neuronal disorders, such as chronic pain, where elevated NO is a contributing factor.

The DDAH/ADMA/NOS pathway.

An increasing number of reports in the literature indicate that endogenously produced inhibitors of nitric oxide synthase (NOS), particularly asymmetric dimethylarginine (ADMA) regulate nitric oxide generation in numerous disease states. Two dimethylarginine dimethylaminohydrolase (DDAH) enzymes metabolise ADMA. We and others have postulated that activity of DDAH is a key determinant of ADMA levels in vivo. This review summarises recent advances in the regulation and function of DDAH enzymes and its role in the regulation of nitric oxide generation.

Overexpression of GTP cyclohydrolase 1 feedback regulatory protein is protective in a murine model of septic shock.

Overproduction of nitric oxide (NO) by inducible NO synthase contributes toward refractory hypotension, impaired microvascular perfusion, and end-organ damage in septic shock patients. Tetrahydrobiopterin (BH4) is an essential NOS cofactor. GTP cyclohydrolase 1 (GCH1) is the rate-limiting enzyme for BH4 biosynthesis. Under inflammatory conditions, GCH1 activity and hence BH4 levels are increased, supporting pathological NOS activity. GCH1 activity can be controlled through allosteric interactions with GCH1 feedback regulatory protein (GFRP). We investigated whether overexpression of GFRP can regulate BH4 and NO production and attenuate cardiovascular dysfunction in sepsis. Sepsis was induced in mice conditionally overexpressing GFRP and wild-type littermates by cecal ligation and puncture. Blood pressure was monitored by radiotelemetry, and mesenteric blood flow was quantified by laser speckle contrast imaging. Blood biochemistry data were obtained using an iSTAT analyzer, and BH4 levels were measured in plasma and tissues by high-performance liquid chromatography. Increased BH4 and NO production and hypotension were observed in all mice, but the extents of these pathophysiological changes were attenuated in GFRP OE mice. Perturbations in blood biochemistry were similarly attenuated in GFRP OE compared with wild-type controls. These results suggest that GFRP overexpression regulates GCH1 activity during septic shock, which in turn limits BH4 bioavailability for iNOS. We conclude that the GCH1-GFRP axis is a critical regulator of BH4 and NO production and the cardiovascular derangements that occur in septic shock.

Immunolocalisation and activity of DDAH I and II in the heart and modification post-myocardial infarction.

Asymmetric dimethylarginine (ADMA) and N(G) monomethyl-L-arginine (L-NMMA) are endogenous inhibitors of nitric oxide synthases (NOS) and their local concentration is determined by the activity of dimethylarginine dimethylaminohydrolases (DDAHs). The current study in male Wistar rats was designed to immunolocalise DDAH I and II in relation to NOS and to investigate changes in distribution, activity and ADMA content in the acute period following myocardial infarction (MI) resulting from coronary artery ligation. Seven days after the coronary artery ligation, L-Arg and methylated arginine content, as well as DDAH activity were determined in homogenates of left ventricular (LV) infarct and border. The distribution of immunoreactive DDAH I, DDAH II, eNOS and iNOS were determined in sections of LV. In healthy hearts, DDAH I was absent, however, DDAH II was localized to endothelium and endocardium with a similar distribution to that of eNOS. Following MI, LV DDAH activity was increased (to 210+/-19% of control, P<0.05). Both DDAH I and DDAH II proteins were detected in peri-infarct cardiomyocytes, while DDAH II immunoreactivity was additionally localized to infiltrating inflammatory cells and blood vessels in the healing infarct. Both plasma and LV concentrations of the DDAH substrate, ADMA, were increased post-MI, although the ratio of Arg:ADMA was retained in the LV post-MI relative to sham operated controls. In conclusion, DDAH II has a distribution similar to eNOS in healthy myocardium. The increased levels and activity of DDAH I and DDAH II enzymes following myocardial infarction suggest a potential role for them in local protection of NOS enzymes from inhibition by methylated arginines during infarct healing.

Modulation of Rac1 activity by ADMA/DDAH regulates pulmonary endothelial barrier function.

Endogenously produced nitric oxide synthase inhibitor, asymmetric methylarginine (ADMA) is associated with vascular dysfunction and endothelial leakage. We studied the role of ADMA, and the enzymes metabolizing it, dimethylarginine dimethylaminohydrolases (DDAH) in the regulation of endothelial barrier function in pulmonary macrovascular and microvascular cells in vitro and in lungs of genetically modified heterozygous DDAHI knockout mice in vivo. We show that ADMA increases pulmonary endothelial permeability in vitro and in in vivo and that this effect is mediated by nitric oxide (NO) acting via protein kinase G (PKG) and independent of reactive oxygen species formation. ADMA-induced remodeling of actin cytoskeleton and intercellular adherens junctions results from a decrease in PKG-mediated phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and a subsequent down-regulation of Rac1 activity. The effects of ADMA on endothelial permeability, Rac1 activation and VASP phosphorylation are prevented by overexpression of active DDAHI and DDAHII, whereas inactive DDAH mutants have no effect. These findings demonstrate for the first time that ADMA metabolism critically determines pulmonary endothelial barrier function by modulating Rac1-mediated remodeling of the actin cytoskeleton and intercellular junctions.

The ADMA/DDAH pathway is a critical regulator of endothelial cell motility.

Asymmetric dimethylarginine (ADMA) is an inhibitor of nitric oxide production associated with abnormal blood vessel growth and repair, however, the mechanism of action of ADMA is not well understood. We studied the role of exogenous and endogenous ADMA in the regulation of cell motility and actin cytoskeleton in porcine pulmonary endothelial cells (PAECs) and pulmonary microvascular endothelial cells (PMECs) from knockout mice that lack one of the enzyme metabolising ADMA, dimethylarginine dimethylaminohydrolase I (DDAHI) as well as endothelial cells overexpressing DDAH in vitro. We show that ADMA induced stress fibre and focal adhesion formation and inhibited cell motility in primary pulmonary endothelial cells. The effects of ADMA depended on the activity of RhoA and Rho kinase and were reversed by overexpression of DDAH, nitric oxide donors and protein kinase G activator, 8-bromo-cGMP. ADMA also inhibited the activities of Rac1 and Cdc42 in cells but these changes had a minor effect on cell motility. Endogenous ADMA increased RhoA activity and inhibited cell motility in PMECs from DDAHI knockout mice and inhibited angiogenesis in vitro. These results are the first demonstration that metabolism of cardiovascular risk factor ADMA regulates endothelial cell motility, an important factor in angiogenesis and vascular repair.

Discovery of inhibitors of the pentein superfamily protein dimethylarginine dimethylaminohydrolase (DDAH), by virtual screening and hit analysis.

An efficient process for the discovery of inhibitors of DDAH enzymes, without the requirement for high throughput screening, is described. Physicochemical filtering of a 308,000-compound library according to drug likeness followed by reciprocal nearest neighbour selection produced a representative subset of 35,000 compounds. Virtual screening on a dual processor PC using FlexX, followed by biological screening, identified two hit series. Similarity searches of commercial databases and chemical re-synthesis of pure compounds resulted in SR445 as an inhibitor of Pseudomonas aeruginosa DDAH at 2 microM.

The DDAH-ADMA-NOS pathway.

An increasing number of reports in the literature indicate that endogenously produced inhibitors of nitric oxide synthase (NOS),particularly asymmetric dimethylarginine (ADMA), regulate nitric oxide generation in disease states. This article describes the biology of ADMA and the implications for cardiovascular physiology and pathophysiology.

Dimethylarginine dimethylaminohydrolase activity modulates ADMA levels, VEGF expression, and cell phenotype.

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and is metabolised by dimethylarginine dimethylaminohydrolase (DDAH). Elevated levels of circulating ADMA correlate with various cardiovascular pathologies less is known about the cellular effects of altered DDAH activity. We modified DDAH activity in cells and measured the changes in ADMA levels, morphological phenotypes on Matrigel, and expression of vascular endothelial growth factor (VEGF). DDAH over-expressing ECV304 cells secreted less ADMA and when grown on Matrigel had enhanced tube formation compared to untransfected cells. VEGF mRNA levels were 2.1-fold higher in both ECV304 and murine endothelial cells (sEnd.1) over-expressing DDAH. In addition the DDAH inhibitor, S-2-amino-4(3-methylguanidino)butanoic acid (4124W 1mM), markedly reduced human umbilical vein endothelial cell tube formation in vitro. We have found that upregulating DDAH activity lowers ADMA levels, increases the levels of VEGF mRNA in endothelial cells, and enhances tube formation in an in vitro model, whilst blockade of DDAH reduces tube formation.