Dimethylarginine dimethylaminohydrolase-2 overexpression improves impaired nitric oxide synthesis of endothelial cells induced by glycated protein

HIF-1α and Nrf2 regulates hypoxia induced overexpression of DDAH1 through promoter activation in prostate cancer

Dimethylarginine dimethylaminohydrolase-1 (DDAH1) is overexpressed in prostate cancer (PCa) and promotes PCa progression in in vivo through the ADMA-NO pathway by degrading nitric oxide synthase (NOS) inhibitors such as asymmetric dimethylarginine (ADMA) and monomethylamine arginine (L-NMMA). In this study, we investigated the molecular mechanism involved in the overexpression of DDAH1 in PCa and examined its potential role as a therapeutic target. We observed that DDAH1expression is elevated in PCa (PC3, LNCaP, and DU145) cell lines under hypoxia. ChIP and reporter assay results confirmed that DDAH1 expression is positively regulated by HIF-1α through directly binding to the hypoxia response elements (HRE) located within the promoter region between - 1242/- 1238 upstream of its transcription start site (TSS). Under hypoxia, HIF-1α is translocated into the nucleus and activates its target gene expression in PC3 cells. Interestingly, in the event of HIF-1α inhibition or siRNA-mediated knockdown, an alternative transcription factor Nrf2 promotes DDAH1 expression through antioxidant response elements (AREs) on its promoter. ChIP assay results showed that Nrf2 binds to AREs located between -1016 / -1008 bp from the TSS of DDAH1. Furthermore, knockdown of PCa therapeutic target HSP90, an essential co-factor for both HIF-1α and Nrf2 causes attenuation of hypoxia induced DDAH1 overexpression in PCa cells. These results demonstrate that hypoxia induced upregulation of DDAH1 expression is positively regulated by HIF-1α and Nrf2 in association with HSP90. Therefore, targeting tumor angiogenesis promoting DDAH1 along with standard androgen receptor (AR) targeted therapy may offer an effective strategy to prevent PCa progression.

Genetics of PlGF plasma levels highlights a role of its receptors and supports the link between angiogenesis and immunity

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor family and is involved in bone marrow-derived cell activation, endothelial stimulation and pathological angiogenesis. High levels of PlGF have been observed in several pathological conditions especially in cancer, cardiovascular, autoimmune and inflammatory diseases. Little is known about the genetics of circulating PlGF levels. Indeed, although the heritability of circulating PlGF levels is around 40%, no studies have assessed the relation between PlGF plasma levels and genetic variants at a genome-wide level. In the current study, PlGF plasma levels were measured in a population-based sample of 2085 adult individuals from three isolated populations of South Italy. A GWAS was performed in a discovery cohort (N = 1600), followed by a de novo replication (N = 468) from the same populations. The meta-analysis of the discovery and replication samples revealed one signal significantly associated with PlGF circulating levels. This signal was mapped to the PlGF co-receptor coding gene NRP1, indicating its important role in modulating the PlGF plasma levels. Two additional signals, at the PlGF receptor coding gene FLT1 and RAPGEF5 gene, were identified at a suggestive level. Pathway and TWAS analyses highlighted genes known to be involved in angiogenesis and immune response, supporting the link between these processes and PlGF regulation. Overall, these data improve our understanding of the genetic variation underlying circulating PlGF levels. This in turn could lead to new preventive and therapeutic strategies for a wide variety of PlGF-related pathologies.

Endothelial Dysfunction Driven by Hypoxia-The Influence of Oxygen Deficiency on NO Bioavailability

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. The initial stage of CVDs is characterized by endothelial dysfunction, defined as the limited bioavailability of nitric oxide (NO). Thus, any factors that interfere with the synthesis or metabolism of NO in endothelial cells are involved in CVD pathogenesis. It is well established that hypoxia is both the triggering factor as well as the accompanying factor in cardiovascular disease, and diminished tissue oxygen levels have been reported to influence endothelial NO bioavailability. In endothelial cells, NO is produced by endothelial nitric oxide synthase (eNOS) from L-Arg, with tetrahydrobiopterin (BH₄) as an essential cofactor. Here, we discuss the mechanisms by which hypoxia affects NO bioavailability, including regulation of eNOS expression and activity. What is particularly important is the fact that hypoxia contributes to the depletion of cofactor BH₄ and deficiency of substrate L-Arg, and thus elicits eNOS uncoupling-a state in which the enzyme produces superoxide instead of NO. eNOS uncoupling and the resulting oxidative stress is the major driver of endothelial dysfunction and atherogenesis. Moreover, hypoxia induces impairment in mitochondrial respiration and endothelial cell activation; thus, oxidative stress and inflammation, along with the hypoxic response, contribute to the development of endothelial dysfunction.

Treatment of atherosclerosis through transplantation of endothelial progenitor cells overexpressing dimethylarginine dimethylaminohydrolase (DDAH) in rabbits

BACKGROUND

Endothelial dysfunction is a key event in the development of vascular diseases, including atherosclerosis. Endothelial progenitor cells (EPCs) play an important role in vascular repair. Decreased dimethylarginine dimethylaminohydrolase (DDAH) activity is observed in several pathological conditions, and it is associated with an increased risk of vascular disease. We hypothesized that bone marrow-derived EPCs and combination therapy with DDAH2-EPCs could reduce plaque size and ameliorate endothelial dysfunction in an atherosclerosis rabbit model.

METHOD

Four groups of rabbits (n = 8 per group) were subjected to a hyperlipidemic diet for a month. After establishing the atherosclerosis model, rabbits received 4 × 10⁶ EPC, EPCs expressing DDAH2, through femoral vein injection, or saline (the control group with basic food and the untreated group). One month after transplantation, plaque thickness, endothelial function, oxidative stress, and inflammatory mRNAs, DDAH, and eNOS function were assessed.

RESULTS

DDAH2-EPCs transplantation (p < 0.05) and EPCs transplantation (p < 0.05) were both associated with a reduction in plaque size compared to the control saline injection. The antiproliferative and antiatherogenic effects of EPCs were further enhanced by the overexpression of DDAH2 (p < 0.05, DDAH2-EPCs vs. EPCs). Furthermore, DDAH2-EPCs transplantation significantly increased endothelium integrity compared to the EPCs transplantation.

CONCLUSION

Transplantation of EPCs overexpressing DDAH2 may enhance the repair of injured endothelium by reducing inflammation and restoring endothelial function. Therefore, pCMV6-mediated DDAH2 gene-transfected EPCs are a potentially valuable tool for the treatment of atherosclerosis.

Asymmetric Dimethylarginine Limits the Efficacy of Simvastatin Activating Endothelial Nitric Oxide Synthase

Background

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase (eNOS), is considered a risk factor for the pathogenesis of cardiovascular diseases. Simvastatin, a lipid‐lowering drug with other pleiotropic effects, has been widely used for treatment of cardiovascular diseases. However, little is known about the effect and underlying molecular mechanisms of ADMA on the effectiveness of simvastatin in the vascular system.

Methods and Results

We conducted a prospective cohort study to enroll 648 consecutive patients with coronary artery disease for a follow‐up period of 8 years. In patients with plasma ADMA level ≥0.49 μmol/L (a cut‐off value from receiver operating characteristic curve), statin treatment had no significant effect on cardiovascular events. We also conducted randomized, controlled studies using in vitro and in vivo models. In endothelial cells, treatment with ADMA (≥0.5 μmol/L) impaired simvastatin‐induced nitric oxide (NO) production, endothelial NO synthase (eNOS) phosphorylation, and angiogenesis. In parallel, ADMA markedly increased the activity of NADPH oxidase (NOX) and production of reactive oxygen species (ROS). The detrimental effects of ADMA on simvastatin‐induced NO production and angiogenesis were abolished by the antioxidant, N‐acetylcysteine, NOX inhibitor, or apocynin or overexpression of dimethylarginine dimethylaminohydrolase 2 (DDAH‐2). Moreover, in vivo, ADMA administration reduced Matrigel plug angiogenesis in wild‐type mice and decreased simvastatin‐induced eNOS phosphorylation in aortas of apolipoprotein E–deficient mice, but not endothelial DDAH‐2‐overexpressed aortas.

Conclusions

We conclude that ADMA may trigger NOX‐ROS signaling, which leads to restricting the simvastatin‐conferred protection of eNOS activation, NO production, and angiogenesis as well as the clinical outcome of cardiovascular events.

ADMA: a specific biomarker for pathologic progress in diabetic microvascular complications?

BACKGROUND

This study highlights the role of glycated hemoglobin (HbA1c), asymmetric demethylargine (ADMA) and N-ϵ-(carboxymethyl)-lysine (CML) in different periods of progress in Type 2 diabetes, and identifies a pathomechanism-based biomarker that is linked not only to the metabolic progresses but also to the underlying angiopathic progresses.

METHODS

Peripheral blood samples from 100 healthy volunteers, 227 subjects with prediabetes, 173 subjects with Type 2 diabetes and 92 subjects with early diabetic microvascular complications were collected and analyzed for HbA1c, ADMA and CML.

RESULTS

Compared to HbA1c and CML, ADMA is the strongest independent predictor and a significantly discriminative receiver operating characteristics profile, clearly distinguishing those with early diabetic microvascular complications.

CONCLUSIONS

ADMA maybe serve as a pathomechanism-based biomarker, predicting the progression of microvascular complications.

Glycated human serum albumin induces NF-κB activation and endothelial nitric oxide synthase uncoupling in human umbilical vein endothelial cells

AIMS

Non-enzymatic glycated proteins could mediate diabetes vascular complications, but the molecular mechanisms are unknown. Our objective was to find new targets involved in the glycated human serum albumin (gHSA)-enhanced extracellular reactive oxygen species (ROS) production in human endothelial cells.

METHODS & RESULTS

Some nuclear factors and phosphorylation cascades were analysed. gHSA activated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which up-regulated NOX4 and P22PHOX and enhanced ROS production. Pharmacological inhibition of NF-κB reversed gHSA-enhanced NOX4 expression and decreased gHSA-induced ROS production in extra- and intracellular spaces. The inhibition of activator protein-1 (AP-1) induced a rise in NOX4 and P22PHOX subunit expression and a down-regulation of endothelial nitric oxide synthase (eNOS). AP-1 inhibition also enhanced extracellular ROS production in the presence of serum albumin, but not with gHSA. These results were explained by the eNOS uncoupling induced by gHSA, also demonstrated in this study. Phosphatidylinositol 3-kinase or mitogen-activated protein kinase kinase 1/2 did not show to be involved in gHSA-induced ROS production.

CONCLUSIONS

All together, the results suggested that gHSA-enhanced ROS production in endothelium is mediated by: 1) NF-κB activation and subsequence up-regulation of NADPH oxidase, 2) eNOS uncoupling. AP-1, although is not directly affected by gHSA, is another target for regulating NADPH oxidase and eNOS expression in endothelial cells.

Involvement of increased endogenous asymmetric dimethylarginine in the hepatic endoplasmic reticulum stress of type 2 diabetic rats

Objective

Increasing evidence suggested that endoplasmic reticulum (ER) stress contributes to insulin resistance, which plays an important role in the development of type 2 diabetes mellitus (T2DM). Accumulation of endogenous nitric oxide synthase (NOS) inhibitor, asymmetric dimethylarginine (ADMA), is associated with insulin resistance, T2DM, and diabetic cardiovascular complications, although the mechanisms have not been elucidated. This study was to determine whether elevated endogenous ADMA is involved in hepatic ER stress of type 2 diabetic rats, verify their causal relationship, and elucidate the potential mechanism underlying ADMA induced ER stress in rat hepatocytes.

Methods

Immunoglobulin binding protein (Bip) transcription, eukaryotic initiation factor 2α kinase (eIF2α) phosphorylation, X box-binding protein-1 (XBP-1) mRNA splicing and C/EBP homologues protein (CHOP) expression were measured to reflect ER stress. Contents of ADMA and nitrite/nitrate as well as activities or expression of NOS and dimethylarginine dimethylaminohydrolase (DDAH) were detected to show the changes in DDAH/ADMA/NOS/NO pathway. The lipid peroxidation product malondialdehyde content and antioxidant enzyme superoxide dismutase activity were analyzed to evaluate oxidative stress.

Results

ER stress was provoked in the liver of type 2 diabetic rats, as expressed by increases of Bip transcription, eIF2α phosphorylation, XBP-1 splicing and CHOP expression, all of which were in parallel with the elevation of serum ADMA, suppression of NO generation, NOS and DDAH activities in the liver. Exposure of hepatocytes to ADMA or hydrogen peroxide also induced ER stress, which was associated with the inhibition of NO production and increase of oxidative stress. Treatment of hepatocytes with antioxidant pyrrolidine dithiocarbamate not only decreased ADMA-induced oxidative stress and inhibition of NO production but also reduced ADMA-triggered ER stress.

Conclusions

These results indicate that increased endogenous ADMA contributes to hepatic ER stress in type 2 diabetic rats, and the mechanism underlying ADMA-induced ER stress may relate to oxidative stress via NOS uncoupling.

Obeticholic acid, a farnesoid X receptor agonist, improves portal hypertension by two distinct pathways in cirrhotic rats

The farnesoid X receptor (FXR) is a nuclear bile acid receptor involved in bile acid homeostasis, hepatic and intestinal inflammation, liver fibrosis, and cardiovascular disease. We studied the effect of short-term treatment with obeticholic acid (INT-747), a potent selective FXR agonist, on intrahepatic hemodynamic dysfunction and signaling pathways in different rat models of cirrhotic portal hypertension (PHT). For this, thioacetamide (TAA)-intoxicated and bile-duct-ligated (BDL) rats were used as models. After gavage of two doses of 30 mg/kg of INT-747 or vehicle within 24 hours, in vivo hemodynamics were assessed. Additionally, we evaluated the direct effect of INT-747 on total intrahepatic vascular resistance (IHVR) and intrahepatic vascular tone (endothelial dysfunction and hyperresponsiveness to methoxamine) by means of an in situ liver perfusion system and on hepatic stellate cell contraction in vitro. FXR expression and involved intrahepatic vasoactive pathways (e.g., endothelial nitric oxide synthase [eNOS], Rho-kinase, and dimethylarginine dimethylaminohydrolase [DDAH]) were analyzed by immunohistochemistry, reverse-transcriptase polymerase chain reaction, or western blotting. In both cirrhotic models, FXR expression was decreased. Treatment with INT-747 in TAA and BDL reactivated the FXR downstream signaling pathway and decreased portal pressure by lowering total IHVR without deleterious systemic hypotension. In the perfused TAA and BDL cirrhotic liver, INT-747 improved endothelial vasorelaxation capacity, but not hyperresponsiveness. In both groups, this was associated with an increased eNOS activity, which, in TAA, related to down-regulation of Rho-kinase and in BDL to up-regulation of DDAH-2.

CONCLUSION

FXR agonist INT-747 improves PHT in two different rat models of cirrhosis by decreasing IHVR. This hemodynamic effect relates to increased intrahepatic eNOS activity by pathways that differ depending on the etiology of cirrhosis.

Protection of DDAH2 overexpression against homocysteine-induced impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells

BACKGROUND/AIMS

Homocysteine-induced endothelial dysfunction favors the development of cardiovascular diseases through accumulation of endogenous nitric oxide (NO) synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA). Dimethylarginine dimethylaminohydrolase 2 (DDAH2) is the major enzyme for the degradation of ADMA in endothelial cells. The purpose of this study was to determine whether suppressed DDAH2 expression contributed to impairments of DDAH/ADMA/NOS/NO pathway induced by homocysteine in endothelial cells and whether DDAH2 overexpression could prevent endothelial cell dysfunction caused by homocysteine.

METHODS

Liposome-mediated transfection of endothelial cells was performed to establish the cell line of DDAH2 overexpression. After treatment of cells with 1 mmol/L homocysteine for 24 h, the transcription and expression of DDAH1 and DDAH2, DDAH and NOS activities as well as ADMA and NO concentrations were measured.

RESULTS

Treatment of endothelial cells with homocysteine significantly suppressed the transcription and expression of DDAH2 but not DDAH1. This suppression was associated with the declined DDAH activity, increased ADMA accumulation, inhibited NOS activity and decreased NO production in endothelial cells. DDAH2 overexpression not only resisted homocysteine-induced decline of DDAH activity, but also decreased the accumulation of endogenous ADMA, subsequently attenuated the reductions of NOS activity and NO production induced by homocysteine.

CONCLUSIONS

These results indicate that suppression of DDAH2 expression is a culprit for homocysteine-induced impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells, and therapeutic manipulation of DDAH2 expression may be a promising strategy for preventing endothelial dysfunction and cardiovascular diseases associated with hyperhomocysteinemia.

Pilot study of the association of the DDAH2 -449G polymorphism with asymmetric dimethylarginine and hemodynamic shock in pediatric sepsis

Background

Genetic variability in the regulation of the nitric oxide (NO) pathway may influence hemodynamic changes in pediatric sepsis. We sought to determine whether functional polymorphisms in DDAH2, which metabolizes the NO synthase inhibitor asymmetric dimethylarginine (ADMA), are associated with susceptibility to sepsis, plasma ADMA, distinct hemodynamic states, and vasopressor requirements in pediatric septic shock.

Methodology/Principal Findings

In a prospective study, blood and buccal swabs were obtained from 82 patients ≤18 years (29 with severe sepsis/septic shock plus 27 febrile and 26 healthy controls). Plasma ADMA was measured using tandem mass spectrometry. DDAH2 gene was partially sequenced to determine the −871 6g/7g insertion/deletion and −449G/C single nucleotide polymorphisms. Shock type (“warm” versus “cold”) was characterized by clinical assessment. The −871 7g allele was more common in septic (17%) then febrile (4%) and healthy (8%) patients, though this was not significant after controlling for sex and race (p = 0.96). ADMA did not differ between −871 6g/7g genotypes. While genotype frequencies also did not vary between groups for the −449G/C SNP (p = 0.75), septic patients with at least one −449G allele had lower ADMA (median, IQR 0.36, 0.30–0.41 µmol/L) than patients with the −449CC genotype (0.55, 0.49–0.64 µmol/L, p = 0.008) and exhibited a higher incidence of “cold” shock (45% versus 0%, p = 0.01). However, after controlling for race, the association with shock type became non-significant (p = 0.32). Neither polymorphism was associated with inotrope score or vasoactive infusion duration.

Conclusions/Significance

The −449G polymorphism in the DDAH2 gene was associated with both low plasma ADMA and an increased likelihood of presenting with “cold” shock in pediatric sepsis, but not with vasopressor requirement. Race, however, was an important confounder. These results support and justify the need for larger studies in racially homogenous populations to further examine whether genotypic differences in NO metabolism contribute to phenotypic variability in sepsis pathophysiology.

Dimethylarginine dimethylaminohydrolase 2, a newly identified mitochondrial protein modulating nitric oxide synthesis in normal human chondrocytes

OBJECTIVE

The mitochondrion is known to be important to chondrocyte survival. This study was undertaken to analyze protein expression profiles in chondrocyte mitochondria that are affected by interleukin-1β (IL-1β).

METHODS

Normal human chondrocytes were isolated from knee cartilage obtained at autopsy from subjects with no history of joint disease. Cells were incubated for 48 hours with or without IL-1β (5 ng/ml). Proteins were separated by 2-dimensional electrophoresis and stained with Sypro Ruby, Coomassie brilliant blue, or silver. Qualitative and quantitative analyses were carried out using PDQuest software. Proteins were identified by mass spectrometry using matrix-assisted laser desorption ionization-time-of-flight/time-of-flight technology. The proteomic results were validated by real-time polymerase chain reaction, Western blotting, and microscopy. Nitric oxide (NO) was quantified using Griess reagent.

RESULTS

Comparative analysis revealed differential expression of signal transduction proteins that regulate cytoskeleton, transcription, metabolic, and stress-related pathways. In total extracts, dimethylarginine dimethylaminohydrolase 2 (DDAH-2) did not show any change in expression after stimulation with IL-1β. However, in mitochondrial extracts, DDAH-2 expression was significantly increased after exposure to IL-1β. Conventional immunofluorescence and confocal microscopy revealed the presence of DDAH-2 in the mitochondria of IL-1β-stimulated chondrocytes. These results were reproducible in cartilage explants treated with IL-1β. In addition, we demonstrated that inhibition of the expression of DDAH-2, as well as interruption of its translocation to the mitochondria, reduced the NO production induced by IL-1β. DDAH-2 protein expression was higher in osteoarthritic (OA) cartilage than in normal cartilage.

CONCLUSION

In the present study, the presence of DDAH-2 in normal human chondrocytes and cartilage was identified for the first time. DDAH-2 could play an important role in IL-1β-induced NO production and in OA pathogenesis.

Nitric oxide, a janus-faced therapeutic target for diabetic microangiopathy-Friend or foe?

Accelerated atherosclerosis and microvascular complications are the leading causes of coronary heart disease, end-stage renal failure, acquired blindness and a variety of neuropathy, which could account for disabilities and high mortality rates in patients with diabetes. As the prevalence of diabetes has risen to epidemic proportions worldwide, diabetic vascular complications have now become one of the most challenging health problems. Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes in humans. NO not only inhibits the inflammatory-proliferative reactions in vascular wall cells, but also exerts anti-thrombogenic and endothelial cell protective properties, all of which could potentially be exploited as a therapeutic option for the treatment of vascular complications in diabetes. However, high amounts of NO produced by inducible NO synthase (iNOS) and/or peroxynitrite (ONOO(-)), a reactive intermediate of NO with superoxide anion are involved in pro-inflammatory reactions and tissue damage as well. This implies that NO is a janus-faced molecule and acts as a double-edged sword in vascular complications in diabetes. Further, NO is synthesized from l-arginine via the action of NO synthase (NOS), while NOS is blocked by endogenous l-arginine analogues such as asymmetric dimethylarginine (ADMA), a naturally occurring amino acid which is found in the plasma and various tissues. These findings suggest that amounts of NO locally produced, oxidative stress conditions and level of ADMA could determine the beneficial and detrimental effects of NO on vascular complications in diabetes. In this paper, we review the janus-faced aspects of NO in diabetic microangiopathy.

Positive association of serum levels of advanced glycation end products and high mobility group box-1 with asymmetric dimethylarginine in nondiabetic chronic kidney disease patients

There is accumulating evidence that engagement of the receptor for advanced glycation end products (RAGE) with ligands such as advanced glycation end products (AGEs) and high mobility group box-1 (HMGB-1) elicits vascular inflammation, thus contributing to the increased risk for cardiovascular disease. Furthermore, enhanced accumulation of asymmetric dimethylarginine (ADMA) plays a role in cardiovascular disease in chronic kidney disease (CKD) patients. However, the relationships among serum levels of AGEs, HMGB-1, soluble form of RAGE (sRAGE), and ADMA are largely unknown. The aim of the present study is to determine their relationships in CKD patients. Twenty nondiabetic normotensive CKD patients with dyslipidemia and 20 age- and sex-matched healthy controls were enrolled. All subjects underwent determination of blood chemistries; urinary proteinuria; and serum levels of AGEs, HMGB-1, sRAGE, and ADMA. Serum AGE, HMGB-1, sRAGE, and ADMA levels in CKD patients were significantly higher than those in control subjects. Circulating levels of AGEs in CKD patients were positively associated with sRAGE and ADMA, and HMGB-1 with ADMA, but not sRAGE. There were no significant associations among these markers and serum creatinine, estimated glomerular filtration rate, proteinuria, and lipid levels. In multiple regression analyses, AGEs and HMGB-1 were independently correlated with ADMA. The present study demonstrated that AGE and sRAGE levels were correlated with each other and that AGEs and HMGB-1 were independently associated with ADMA in nondiabetic CKD patients. Elevation of the RAGE ligands may enhance ADMA levels, suggesting the active involvement of AGE/HMGB-1-RAGE-ADMA axis in CKD patients.

Ex vivo gene transferring of human dimethylarginine dimethylaminohydrolase-2 improved endothelial dysfunction in diabetic rat aortas and high glucose-treated endothelial cells

OBJECTIVES

Elevated level of asymmetric dimethylarginine (ADMA) is an independent risk factor for endothelial dysfunction. Dimethylarginine dimethylaminohydrolase (DDAH) is the key enzyme responsible for the degradation of endogenous ADMA. The purposes of this study were to determine whether suppressed DDAH2 expression would implicate in endothelial dysfunction associated with diabetes mellitus and further to investigate whether adenovirus-mediated DDAH2 gene overexpression could improve the hyperglycemia-induced endothelial dysfunction.

METHODS

Diabetic model was induced by intraperitoneal injection of streptozotocin to male Sprague-Dawley rats. Recombinant adenoviral vector encoding human DDAH2 gene driven by a cytomegalovirus promoter was constructed to overexpress hDDAH2 gene in isolated rat aortas and endothelial cells. Changes in DDHA/ADMA/nitric oxide (NO) pathway in diabetic rats and high glucose-treated endothelial cells were examined.

RESULTS

DDAH2 expression was distinctly suppressed, which was accompanied by inhibited DDAH activity and impaired endothelium-dependent relaxation in aortas, and elevated ADMA concentrations in serum of diabetic rats compared to control rats. Suppressions of DDAH2 expression and DDAH activity, accumulation of ADMA, and inhibition of NO synthesis were observed in high glucose-treated endothelial cells. DDAH2 overexpression not only improved endothelial dysfunction in diabetic aortas but also attenuated hyperglycemia-induced changes in DDAH/ADMA//NO pathway in endothelial cells.

CONCLUSION

These results indicate that suppression of DDAH2 expression contributes to hyperglycemia-induced endothelial dysfunction, which can be improved by DDAH2 overexpression. This study suggests that targeted modulation of DDAH2 gene in vascular endothelium may be a novel approach for the treatment of endothelial dysfunction in diabetes mellitus.

Glycemic control modulates arginine and asymmetrical-dimethylarginine levels during critical illness by preserving dimethylarginine-dimethylaminohydrolase activity

In the context of the hypercatabolic response to stress, critically ill patients reveal hyperglycemia and elevated levels of asymmetrical-dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthases. Both hyperglycemia and elevated ADMA levels predict increased morbidity and mortality. Tight glycemic control by intensive insulin therapy lowers circulating ADMA levels, and improves morbidity and mortality. Methylarginines are released from proteins during catabolism. ADMA is predominantly cleared by the enzyme dimethylarginine-dimethylaminohydrolase (DDAH) in different tissues, whereas its symmetrical isoform (SDMA) is cleared via the kidneys. Therefore, glycemic control or glycemia-independent actions of insulin on protein breakdown and/or on DDAH activity resulting in augmented ADMA levels may explain part of the clinical benefit of intensive insulin therapy. Therefore, we investigated in our animal model of prolonged critical illness the relative impact of maintaining normoglycemia and of glycemia-independent action of insulin over 7 d in a four-arm design on plasma and tissue levels of ADMA and SDMA, on proteolysis as revealed by surrogate parameters as changes of body weight, plasma urea to creatinine ratio, and plasma levels of SDMA, and on tissue DDAH activity. We found that ADMA levels remained normal in the two normoglycemic groups and increased in hyperglycemic groups. SDMA levels in the investigated tissues remained largely unaffected. The urea to creatinine ratio indicated reduced proteolysis in all but normoglycemic/normal insulin animals. DDAH activity deteriorated in hyperglycemic compared with normoglycemic groups. Insulin did not affect this finding independent of glycemic control action. Conclusively, maintenance of normoglycemia and not glycemia-independent actions of insulin maintained physiological ADMA plasma and tissue levels by preserving physiological DDAH activity.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.