[Show abstract][Hide abstract] ABSTRACT: Even though ˪-arginine (ARG) derivatives can predict cardiovascular mortality, their role as atherosclerotic biomarkers is unclear. We tested the hypothesis if asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and the sum of both (DMA) are positively, while ARG and ARG/ADMA ratio are inversely associated with carotid intima-media thickness (cIMT) and atherosclerotic plaque in the carotid artery.
Cross-sectional data of 1999 subjects (age: 45-81 years; 48.2% ♀) from the population-based Study of Health in Pomerania (SHIP-0) was used. Analysis of variance and logistic regression models were calculated and all adjusted models were corrected for sex, age, smoking status, waist-to-hip ratio and estimated glomerular filtration rate. Increased cIMT (>75th age-sex specific percentile) was found in 517 subjects (25.7%), while atherosclerotic plaque was detected in 1413 subjects (70.4%). SDMA tertiles were significantly positively associated with larger cIMT among subjects with high SDMA levels [>66th: 0.82 (95%-CI 0.80; 0.85) mm]. High SDMA levels were related to a higher odds ratio (OR) of increased cIMT [OR 1.39 (95%-CI 1.08; 1.79)]. Furthermore, ARG was positively associated with atherosclerotic plaques [OR 1.41 (95%-CI 1.07; 1.85)]. No relation was found for ADMA and atherosclerosis.
In conclusion, the hypothesis of a positive association between SDMA with an increased cIMT was confirmed. Unexpectedly, ARG was positively related to atherosclerotic plaque. In view of these inconsistent findings, the impact of ARG derivatives as atherosclerotic biomarkers deserves further research.
[Show abstract][Hide abstract] ABSTRACT: Introduction and Aims: Induced pluripotent stem (iPS) cells are adult cells which have been transcriptionally reprogrammed to an embryonic stem
(ES) cell-like state. iPS cells from patients have dual value as a laboratory resource for studying human pathophysiology
and as a potential source of immunocompatible replacement tissue. As proof-of-principle for the application of iPS cells for
kidney disease research, we tested the ability of iPS cells to model polycystic kidney disease (PKD), a leading cause of kidney
failure, and to differentiate into human kidney cells.
Methods: Primary fibroblasts with characterized mutations from autosomal dominant (ADPKD) and autosomal recessive (ARPKD) patients,
or healthy control patients, were reprogrammed into iPS cells by retroviral expression of OCT4, SOX2, KLF4, and c-myc. PKD
and control iPS cells were quantitatively evaluated for PKD disease gene expression at the primary cilium, an antenna-like
sensory organelle central to PKD pathophysiology. To determine their potential for kidney regeneration, iPS cells were treated
with a panel of growth factors under serum-free conditions and screened for differentiation into embryonic and adult kidney
Results: The derived iPS cells demonstrated extensive self-renewal and differentiation into diverse somatic cell types and tissues.
PKD and control iPS cells elaborated primary cilia and expressed polycystin-1 (PC1), PC2, and fibrocystin/polyductin, the
proteins in which PKD mutations are found. Importantly, iPS and descendant epithelial cells from all three ADPKD patients
expressed significantly reduced quantities of PC2 at the primary cilium, as assessed by quantitative immunofluorescence. Gene
sequencing revealed mutations in PC1, not PC2, suggesting that PC1 regulates PC2 trafficking to cilia. Consistent with this
hypothesis, overexpression of wild-type but not mutant PC1 significantly increased ciliary PC2 levels. Sequential treatment
of ES or iPS cells with CHIR99021 (a GSK3beta inhibitor), FGF2, and retinoic acid induced differentiation into cells expressing
markers typical of intermediate mesoderm (PAX2+LHX1+), nephrogenic cap mesenchyme (SIX2+WT1+SALL1+), and proximal tubule (KSP+LTL+),
indicating potential for renal lineage differentiation.
Conclusions: Ciliary PC2 mislocalization is an early and highly penetrant phenotype in ADPKD iPS cells, which can be screened in vitro
to identify candidate therapeutics. PC1 overexpression rescues PC2 localization, suggesting a possible therapeutic approach.
Derivation of embryonic and adult kidney cells from iPS cells provides a potential source of cells for transplant which would
be 100% immunocompatible with the original patient. The ability of iPS cells to provide novel mechanistic insights into human
cellular pathophysiology, together with their potential as regenerative cell therapeutics, makes them a powerful new resource
for kidney disease research.
No preview · Article · May 2014 · Nephrology Dialysis Transplantation
[Show abstract][Hide abstract] ABSTRACT: Nitroxyl (HNO) donors have potential benefit in the treatment of heart failure and other cardiovascular diseases. 1-Nitrosocyclohexyl acetate (NCA), a new HNO donor, in contrast to the classical HNO donors Angeli's salt and isopropylamine NONOate predominantly releases HNO and has a longer half-life. This study investigated the vasodilatative properties of NCA in isolated aortic rings, human platelets, and its mechanism of action. NCA was applied on aortic rings isolated from wild-type mice, apolipoprotein E-deficient mice and in endothelial-denuded aorta. The mechanism of action of HNO was examined by applying NCA in the absence and presence of the HNO scavenger GSH and inhibitors of soluble guanylyl cyclase (sGC), adenylyl cyclase (AC), calcitonin gene-related peptide receptor (CGRP) and K+ channels. NCA induced a concentration dependent relaxation (EC50 4.4 µM). This response did not differ between all groups indicating an endothelium-independent relaxation effect. The concentration-response was markedly decreased in presence of excess GSH; while the nitric oxide scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide had no effect. Inhibitors of sGC, CGRP, and voltage-dependent K+ channel each significantly impaired the vasodilatator response to NCA. In contrast, inhibitors of AC, ATP-sensitive K+ channel or high conductance Ca2+-activated K+ channel did not change the effects of NCA. NCA significantly reduced contractile response and platelet aggregation mediated by thromboxane A2 mimetic U-46619 in a cGMP dependent manner. In summary, NCA shows vasoprotective effects and may have a promising profile as a therapeutic agent in vascular dysfunction, warranting further evaluation.
Full-text · Article · Dec 2012 · Journal of Pharmacology and Experimental Therapeutics
[Show abstract][Hide abstract] ABSTRACT: Endothelial dysfunction as assessed by asymmetric dimethylarginine (ADMA) and inflammation has been consistently linked to atherosclerosis, death, and cardiovascular (CV) events in ESRD patients. Inflammation amplifies the effect of ADMA on the severity of atherosclerosis in ESRD patients, but it is still unknown whether inflammation and ADMA interact in the high risk of death and CV events in this population.
In a cohort of 225 hemodialysis patients, we investigated the interaction between inflammatory biomarkers (C-reactive protein and IL-6) and ADMA as predictors of death and CV events over an extended follow-up (13 years).
During follow-up, 160 patients died, and 123 had CV events. With crude and multiple Cox regression analyses, an interaction was found between inflammation biomarkers and ADMA for explaining death and CV events in ESRD patients. The adjusted hazard ratios (HRs) for death (HR, 2.18; 95% confidence interval [CI], 1.34 to 3.54) and CV outcomes (HR, 2.59; 95% CI, 1.47 to 4.55) of patients with C-reactive protein and ADMA above the median were higher than expected in the absence of interaction under the additive model (1.15 and 1.97, respectively) and significantly higher than in patients with only one biomarker above the median. Data analyses carried out by stratifying patients according to IL-6 provided similar results.
These data support the hypothesis that inflammation amplifies the risk of death and CV events associated with high ADMA levels in ESRD. These analyses further emphasize the need for intervention studies to attenuate inflammation and high ADMA levels in this population.
Full-text · Article · Jun 2011 · Clinical Journal of the American Society of Nephrology
[Show abstract][Hide abstract] ABSTRACT: Endothelium plays a crucial role in the maintenance of vascular tone and structure. Endothelial dysfunction is known to precede overt coronary artery disease. A number of cardiovascular risk factors, as well as metabolic diseases and systemic or local inflammation cause endothelial dysfunction. Nitric oxide (NO) is one of the major endothelium derived vaso-active substances whose role is of prime importance in maintaining endothelial homeostasis. Low levels of NO are associated with impaired endothelial function. Asymmetric dimethylarginine (ADMA), an analogue of L-arginine, is a naturally occurring product of metabolism found in human circulation. Elevated levels of ADMA inhibit NO synthesis and therefore impair endothelial function and thus promote atherosclerosis. ADMA levels are increased in people with hypercholesterolemia, atherosclerosis, hypertension, chronic heart failure, diabetes mellitus and chronic renal failure. A number of studies have reported ADMA as a novel risk marker of cardiovascular disease. Increased levels of ADMA have been shown to be the strongest risk predictor, beyond traditional risk factors, of cardiovascular events and all-cause and cardiovascular mortality in people with coronary artery disease. Interventions such as treatment with L-arginine have been shown to improve endothelium-mediated vasodilatation in people with high ADMA levels. However the clinical utility of modifying circulating ADMA levels remains uncertain.
Full-text · Article · May 2010 · Current Cardiology Reviews
[Show abstract][Hide abstract] ABSTRACT: The endogenous inhibitor of nitric oxide synthase (NOs) asymmetrical dimethyl-arginine (ADMA) has been implicated as a possible modulator of inducible NOs during acute inflammation. We examined the evolution in the plasma concentration of ADMA measured at the clinical outset of acute inflammation and after its resolution in a series of 17 patients with acute bacterial infections.
During the acute phase of inflammation/infection, patients displayed very high levels of C-reactive protein (CRP), interleukin-6 (IL-6), procalcitonin and nitrotyrosine. Simultaneous plasma ADMA concentration was similar to that in healthy subjects while symmetric dimethyl-arginine (SDMA) levels were substantially increased and directly related with creatinine. When infection resolved, ADMA rose from 0.62 +/- 0.23 to 0.80 +/- 0.18 micromol/l (+29%, P = 0.01) while SDMA remained unmodified. ADMA changes were independent on concomitant risk factor changes and inversely related with baseline systolic and diastolic pressure. Changes in the ADMA/SDMA ratio were compatible with the hypothesis that inflammatory cytokines activate ADMA degradation.
Resolution of acute inflammation is characterized by an increase in the plasma concentration of ADMA. The results imply that ADMA suppression may actually serve to stimulate NO synthesis or that in this situation plasma ADMA levels may not reflect the inhibitory potential of this methylarginine at the cellular level.
[Show abstract][Hide abstract] ABSTRACT: We investigated the relationship between ADMA plasma levels and endothelium-dependent vasodilation in 36 never-treated essential hypertensives and in 8 normotensive healthy subjects.
It has been demonstrated that endothelium-dependent vasodilatation is impaired in essential hypertension. The potential contribution of asymmetric dimethylarginine (ADMA) to endothelial dysfunction of hypertensive humans has received poor attention.
Endothelial function was measured during intra-arterial infusion of acetylcholine (ACh), alone and during co-infusion of L-arginine, and sodium nitroprusside at increasing doses. Concentrations of ADMA and L-arginine in plasma were measured by high-performance liquid chromatography.
Hypertensive subjects had significantly higher ADMA and L-arginine plasma concentrations than normotensive healthy controls; ACh-stimulated forearm blood flow (FBF) was significantly reduced in hypertensive subjects in comparison to normotensive control subjects (p < 0.0001). Intra-arterial coinfusion of L-arginine induced a further significant enhancement in ACh-stimulated vasodilation in hypertensive patients. In these, ADMA was strongly and inversely associated with the peak increase in FBF. In a multivariate model, only ADMA and L-arginine were independent correlates, accounting for 33.9% and 8.9% of the variability in the peak FBF response to ACh (p < 0.0001), respectively.
The main finding in this study is that in essential hypertensives the L-arginine and endogenous inhibitor of nitric oxide synthase, ADMA, are inversely related to endothelial function.
Full-text · Article · Sep 2005 · Journal of the American College of Cardiology
[Show abstract][Hide abstract] ABSTRACT: Hyperhomocysteinemia is associated with decreased vascular reactivity and increased cardiovascular morbidity. Oxidative stress and reduced NO bioavailability have been proposed as a mechanism for the adverse effects of chronically elevated plasma homocysteine levels. Recent studies suggest that acute elevations of plasma homocysteine may also impair endothelial function and vasodilation, however, the mechanism is not clear. In the present study, we investigated whether moderate hyperhomocysteinemia after methionine loading decreases NO bioavailability, increases oxidative stress, and impairs receptor-mediated NO-dependent venodilation in healthy adults. After oral methionine loading (0.1g/kg), mean homocysteine concentrations increased 3.2-fold, from 6.9 ± 0.5 to 27.8 ± 1.9μmol/l (n = 16), whereas plasma NOx concentrations, an indicator of NO release, were decreased by 12% compared to placebo treatment (P = 0.005). Vitamin E levels in freshly isolated low density lipoprotein (LDL), a sensitive marker of LDL oxidation, and LDL lipid (hydro)peroxide levels were unchanged after methionine loading. Endothelium-dependent venodilation induced by bradykinin was reduced by 18% during hyperhomocysteinemia (P = 0.06). Taken together our data suggest that the reduced NO bioavailability was likely due to decreased NO synthesis and release rather than to NO destruction by oxidative stress.
[Show abstract][Hide abstract] ABSTRACT: Experimental hyperhomocysteinemia after an oral methionine or homocysteine load is associated with impaired nitric oxide-dependent vasodilatation in healthy human beings. However, it remains unproven that this effect is mediated by elevations in plasma homocysteine. There is evidence that an increase in plasma homocysteine may increase the formation of asymmetric dimethylarginine (ADMA), an inhibitor of nitric oxide synthase. The methyl groups within ADMA are derived from the conversion of S-adenosylmethionine to S-adenosylhomocysteine intermediates in the methionine/homocysteine pathway. No previous study has assessed the role of methylation status, its impact on ADMA formation, and their association with endothelial function in healthy human beings. In a randomized, placebo-controlled, crossover study, 10 healthy subjects (mean age, 29.1 ± 3.9 years) were administered an oral dose of methionine (0.1 g/kg), l-homocysteine (0.01 g/kg), N-acetylcysteine (NAC) (0.1 g/kg), or placebo. Endothelial function as assessed by flow-mediated dilatation (FMD) of the brachial artery was impaired after both the methionine and homocysteine load compared with placebo at 4 hours (36 ± 15, 67 ± 23 vs 219 ± 26 μm, respectively, P < .001). N-Acetylcysteine had no effect on flow-mediated dilatation. Plasma total homocysteine was significantly elevated at 4 hours after methionine (23.1 ± 6.2) and homocysteine (41.5 ± 8.9) loading, but significantly reduced after NAC 2.4 ± 0.6 vs 7.1 ± 2.1 μmol/L in the placebo (P < .001). Plasma S- adenosylmethionine/S-adenosylhomocysteine ratio was significantly (P < .001) increased at 4 hours after methionine (10.9 ± 0.7) compared with homocysteine (5.4 ± 0.4), NAC (5.0 ± 0.3), and placebo (6.0 ± 0.5). Plasma ADMA concentrations were not altered by any intervention. Our results suggest that endothelial dysfunction due to methionine or homocysteine loading is not associated with an increase in plasma ADMA or a disruption in methylation status.
[Show abstract][Hide abstract] ABSTRACT: Analogues of L-arginine that are chemically modified at the terminal guanidino nitrogen group, such as N(ω)-monomethy-L-arginine (L-NMMA), have been used for nitric oxide synthase inhibition. However, L-NMMA and other methylated L-arginine analogues are also endogenously formed. Among these, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) have been shown to be the most abundant. Like L-NMMA, ADMA is an inhibitor of NO synthase, whereas SDMA is inactive. ADMA is synthesized by N-methyltransferases, a family of enzymes that methylate L-arginine residues within specific proteins. Free ADMA is released during proteolytic cleavage of methylated proteins; it can be detected in plasma and urine, but its intracellular concentrations appear to be much higher. ADMA is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), and inhibition of DDAH activity has been shown to lead to increased ADMA levels and endothelial dysfunction. Plasma levels of ADMA are elevated in endstage renal failure, in atherosclerosis and hypercholesterolemia, in hypertension, and in heart failure. Although the molecular cause for elevation of ADMA concentration in these diseases has not been fully elucidated, evidence is accumulating that ADMA is one cause of endothelial dysfunction in these diseases. Moreover, it may be a marker or even a risk factor for cardiovascular disease. Therefore, pharmacological modulation of ADMA concentration may be a novel therapeutic target in cardiovascular diseases.
Preview · Article · Jan 2000 · Seminars in Thrombosis and Hemostasis
[Show abstract][Hide abstract] ABSTRACT: There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO). Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthase. ADMA inhibits vascular NO production at concentrations found in pathophysiological conditions (i.e., 3-15 mmol / l); ADMA also causes local vasoconstriction when it is infused intraarterially. The biochemical and physiological pathways related to ADMA are now well understood: dimethylarginines are the result of the degradation of methylated proteins; the methyl group is derived from S-adenosylmethionine. Both ADMA and its regioisomer, SDMA, are eliminated from the body by renal excretion, whereas only ADMA, but not SDMA, is metabolized via hydrolytic degradation to citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). DDAH activity and / or expression may therefore contribute to the pathogenesis of endothelial dysfunction in various diseases. ADMA is increased in the plasma of humans with hypercholesterolemia, atherosclerosis, hypertension, chronic renal failure, and chronic heart failure. Increased ADMA levels are associated with reduced NO synthesis as assessed by impaired endothelium-dependent vasodilation. In several prospective and cross-sectional studies, ADMA evolved as a marker of cardiovascular risk. With our increasing knowledge of the role of ADMA in the pathogenesis of cardiovascular disease, ADMA is becoming a goal for pharmacotherapeutic intervention. Among other treatments, the administration of L-arginine has been shown to improve endothelium-