Asymmetric Dimethylarginine: Clinical Applications in Pediatric Medicine

Genetically encoded fluorescent sensor to monitor intracellular arginine methylation

Arginine methylation (ArgMet), as a post-translational modification, plays crucial roles in RNA processing, transcriptional regulation, signal transduction, DNA repair, apoptosis and liquid-liquid phase separation (LLPS). Since arginine methylation is associated with cancer pathogenesis and progression, protein arginine methyltransferases have gained interest as targets for anti-cancer therapy. Despite considerable process made to elucidate (patho)physiological mechanisms regulated by arginine methylation, there remains a lack of tools to visualize arginine methylation with high spatiotemporal resolution in live cells. To address this unmet need, we generated an ArgMet-sensitive genetically encoded, Förster resonance energy transfer-(FRET) based biosensor, called GEMS, capable of quantitative real-time monitoring of ArgMet dynamics. We optimized these biosensors by using different ArgMet-binding domains, arginine-glycine-rich regions and adjusting the linkers within the biosensors to improve their performance. Using a set of mammalian cell lines and modulators, we demonstrated the applicability of GEMS for monitoring changes in arginine methylation with single-cell and temporal resolution. The GEMS can facilitate the in vitro screening to find potential protein arginine methyltransferase inhibitors and will contribute to a better understanding of the regulation of ArgMet related to differentiation, development and disease.

Evidence for the Benefits of Melatonin in Cardiovascular Disease

The pineal gland is a neuroendocrine gland which produces melatonin, a neuroendocrine hormone with critical physiological roles in the circadian rhythm and sleep-wake cycle. Melatonin has been shown to possess anti-oxidant activity and neuroprotective properties. Numerous studies have shown that melatonin has significant functions in cardiovascular disease, and may have anti-aging properties. The ability of melatonin to decrease primary hypertension needs to be more extensively evaluated. Melatonin has shown significant benefits in reducing cardiac pathology, and preventing the death of cardiac muscle in response to ischemia-reperfusion in rodent species. Moreover, melatonin may also prevent the hypertrophy of the heart muscle under some circumstances, which in turn would lessen the development of heart failure. Several currently used conventional drugs show cardiotoxicity as an adverse effect. Recent rodent studies have shown that melatonin acts as an anti-oxidant and is effective in suppressing heart damage mediated by pharmacologic drugs. Therefore, melatonin has been shown to have cardioprotective activity in multiple animal and human studies. Herein, we summarize the most established benefits of melatonin in the cardiovascular system with a focus on the molecular mechanisms of action.

Protein Methylation in Diabetic Kidney Disease

Chronic kidney disease (CKD) is defined by persistent urine aberrations, structural abnormalities, or impaired excretory renal function. Diabetes is the leading cause of CKD. Their common pathological manifestation is renal fibrosis. Approximately half of all patients with type 2 diabetes and one-third with type 1 diabetes will develop CKD. However, renal fibrosis mechanisms are still poorly understood, especially post-transcriptional and epigenetic regulation. And an unmet need remains for innovative treatment strategies for preventing, arresting, treating, and reversing diabetic kidney disease (DKD). People believe that protein methylation, including histone and non-histone, is an essential type of post-translational modification (PTM). However, prevalent reviews mainly focus on the causes such as DNA methylation. This review will take insights into the protein part. Furthermore, by emphasizing the close relationship between protein methylation and DKD, we will summarize the clinical research status and foresee the application prospect of protein methyltransferase (PMT) inhibitors in DKD treatment. In a nutshell, our review will contribute to a more profound understanding of DKD’s molecular mechanism and inspire people to dig into this field.

Asymmetric Dimethylarginine (ADMA) in Pediatric Renal Diseases: From Pathophysiological Phenomenon to Clinical Biomarker and Beyond

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide (NO) synthase inhibitor, inhibits NO synthesis and contributes to the pathogenesis of many human diseases. In adults, ADMA has been identified as a biomarker for chronic kidney disease (CKD) progression and cardiovascular risk. However, little attention is given to translating the adult experience into the pediatric clinical setting. In the current review, we summarize circulating and urinary ADMA reported thus far in clinical studies relating to kidney disease in children and adolescents, as well as systematize the knowledge on pathophysiological role of ADMA in the kidneys. The aim of this review is also to show the various analytical methods for measuring ADMA and the issues tht need to be addressed before transforming to clinical practice in pediatric medicine. The last task is to suggest that ADMA may not only be suitable as a diagnostic or prognostic biomarker, but also a promising therapeutic strategy to treat pediatric kidney disease in the future.

Impact of Arginine Nutrition and Metabolism during Pregnancy on Offspring Outcomes

By serving as a precursor for the synthesis of nitric oxide, polyamines, and other molecules with biological importance, arginine plays a key role in pregnancy and fetal development. Arginine supplementation is a potential therapy for treating many human diseases. An impaired arginine metabolic pathway during gestation might produce long-term morphological or functional changes in the offspring, namely, developmental programming to increase vulnerability to developing a variety of non-communicable diseases (NCDs) in later life. In contrast, reprogramming is a strategy that shifts therapeutic interventions from adulthood to early-life, in order to reverse the programming processes, which might counterbalance the rising epidemic of NCDs. This review presented the role of arginine synthesis and metabolism in pregnancy. We also provided evidence for the links between an impaired arginine metabolic pathway and the pathogenesis of compromised pregnancy and fetal programming. This was followed by reprogramming strategies targeting the arginine metabolic pathway, to prevent the developmental programming of NCDs. Despite emerging evidence from experimental studies showing that targeting the arginine metabolic pathway has promise as a reprogramming strategy in pregnancy to prevent NCDs in the offspring, these results need further clinical application.

Increased asymmetric dimethylarginine in vitamin B12 deficient adolescents

OBJECTIVE

Vitamin B12 deficiency induces hyper-hyperhomocysteinemia by inhibiting intracellular methionine re-methylation. Hyper-hyperhomocysteinemia increases the risk of atherosclerosis. Asymmetric dimethylarginine is an endogenous inhibitor of nitric oxide synthase and its level elevates in cardiovascular diseases. In this study, we aimed to examine the relationship between asymmetric dimethylarginine and arterial stiffness and atherosclerosis in adolescents with vitamin B12 deficiency.

METHODS

A total of 88 adolescents with age ranging between 11 and 17 years of age were enrolled for this study. Among them, 50 patients had vitamin B12 deficiency 200 pg/ml. In all cases, the levels of asymmetric dimethylarginine were measured with high performance liquid chromatography method. The carotid artery intima media thickness and left ventricular mass index were measured using echocardiography. All these measurements of the study groups were compared.

RESULTS

Both plasma levels of asymmetric dimethylarginine and carotid artery intima media thickness were significantly higher in the vitamin B12 deficiency group than in the control group. Correlation analysis showed significant negative correlation of vitamin B12 with homocysteine, asymmetric dimethylarginine, and carotid artery intima media thickness (p<0.05).

CONCLUSION

Our results suggest that endothelial dysfunction starts in the early stage of adolescent vitamin B12 deficiency, and vitamin B12-deficient adolescents have increased circulating asymmetric dimethylarginine, showing that endothelial dysfunction and increased carotid artery intima media thickness be related to atherosclerosis.

Serum nitric oxide levels in healthy pregnant women: a case- control study in a tertiary facility in Ghana

Background

Pregnancy is associated with significant changes in maternal cardiovascular system which regulates oxygen and nutrient supply to the growing foetus. Nitric oxide, a physiologic vascular smooth muscle relaxant regulates blood flow and therefore may play a role in the cardiovascular changes in pregnancy. The study aimed to determine the levels and changes in maternal serum nitric oxide levels during healthy pregnancy.

Methods

A case-control study was conducted among 32 healthy non-pregnant women as controls and 100 healthy pregnant women (consisting of 33 first trimester, 37 s trimester, and 30 third trimester) as cases. Subjects were consecutively recruited into the study after obtaining an informed consent and meeting the inclusion criteria. Griess Reagent method was used to determine serum nitric oxide levels.

Results

There were no statistically significant difference in the ages and parity of recruited cases and controls. Mean arterial blood pressures were significantly lower (p = 0.009) and serum nitric oxide levels were significantly higher (p < 0.001) in healthy pregnant women compared to healthy non-pregnant women. There was a non-significant progressive increase in serum nitric oxide levels during healthy normal pregnancy.

Conclusions

The finding of a significantly reduced blood pressures and a significant increase in serum nitric oxide levels in healthy pregnancy may suggest a role of nitric oxide in vascular adaptation in pregnancy.

Evaluation of endothelial dysfunction, endothelial plasma markers, and traditional metabolic parameters in children with adiposity

BACKGROUND/PURPOSE

To investigate the correlations among endothelial function assessment parameters, asymmetric dimethylarginine (ADMA)-related biomarkers, and traditional risk factors in adipose children.

METHODS

We enrolled adipose children aged 7-18 years between July 2014 and August 2016 as well as normal-weight controls from the outpatient clinic. Vascular measurements including echocardiography, carotid intima media thickness, pulse wave velocity (PWV), and flow-mediated dilation (FMD) were measured. Venous blood samples including traditional metabolic and endothelial dysfunction parameters were analyzed. Participants were grouped as adipose vs. normal-weight and as adipose with hypertension vs. adipose without hypertension. Clinical presentations, laboratory data, and cardiovascular measurement were compared.

RESULTS

Of the 105 enrolled children, 85 were adipose. Adipose children had higher systolic blood pressure, larger left ventricular (LV) mass, and adverse traditional metabolic biomarkers. FMD was significantly reduced (8.25 (5.32-12.06) % vs. 12.49 (7.18-16.58) %, p = 0.018) in the adipose group. PWV was markedly increased (4.65 (4.2-5.5) m/sec vs. 3.95 (3.38-4.35) m/sec, p < 0.001) in the hypertensive adipose children. Endothelial dysfunction parameters were not significantly changed in this study.

CONCLUSION

Adipose children were at higher risk of hypertension and LV hypertrophy. FMD, PWV and traditional cardiovascular biomarkers can detect subtle vascular changes. Hypertension is an important sign of arterial involvement in adipose children. Although ADMA-related biomarkers were not statistically significant, future studies are needed to confirm its correlation with adiposity and hypertension in children. The early detection and prevention of endothelial dysfunction may decrease the rate of progression to cardiovascular consequences in later life.

Blood asymmetric dimethylarginine and nitrite/nitrate concentrations in short-stature children born small for gestational age with and without growth hormone therapy

Objective

To investigate the basal amino acid metabolism and impact of growth hormone (GH) therapy in short-stature children born small for gestational age (short SGA children).

Methods

In this age-matched case-control study, the basal blood levels of amino acids, asymmetric dimethylarginine (ADMA), and nitrite/nitrate (NOx) were compared between 24 short SGA children and 25 age-matched normal children. Changes in these parameters were assessed for 12 months in 12 short SGA children initiating GH therapy (Group A) and 12 age-matched short SGA children without GH therapy (Group B).

Results

The arginine levels were significantly lower in the short SGA than in normal children. The ADMA levels were significantly higher and NOx levels were significantly lower in the short SGA than normal children. In Group A, the ADMA level was significantly lower and NOx level was significantly higher at 6 months than at baseline. At 12 months, the ADMA level in Group A began to increase, but the NOx level remained the same. Group B showed no significant changes.

Conclusions

This study is the first to show that ADMA is promoted and nitric oxide is suppressed in short SGA children and that GH therapy affects the production of ADMA and nitric oxide.

Interplay between Oxidative Stress and Nutrient Sensing Signaling in the Developmental Origins of Cardiovascular Disease

Cardiovascular disease (CVD) presents a global health burden, despite recent advances in management. CVD can originate from early life by so-called “developmental origins of health and disease” (DOHaD). Epidemiological and experimental evidence supports that early-life insults can induce programming of later CVD. Underlying the DOHaD concept, early intervention may offset programming process to prevent the development of CVD, namely reprogramming. Oxidative stress and nutrient sensing signals have been considered to be major mechanisms of cardiovascular programming, while the interplay between these two mechanisms have not been examined in detail. This review summarizes current evidence that supports the link between oxidative stress and nutrient sensing signaling to cardiovascular programming, with an emphasis on the l-arginine–asymmetric dimethylarginine (ADMA)–nitric oxide (NO) pathway. This review provides an overview of evidence from human studies supporting fetal programming of CVD, insight from animal models of cardiovascular programming and oxidative stress, impact of the l-arginine–ADMA–NO pathway in cardiovascular programming, the crosstalk between l-arginine metabolism and nutrient sensing signals, and application of reprogramming interventions to prevent the programming of CVD. A greater understanding of the mechanisms underlying cardiovascular programming is essential to developing early reprogramming interventions to combat the globally growing epidemic of CVD.

Toxic Dimethylarginines: Asymmetric Dimethylarginine (ADMA) and Symmetric Dimethylarginine (SDMA)

Asymmetric and symmetric dimethylarginine (ADMA and SDMA, respectively) are toxic, non-proteinogenic amino acids formed by post-translational modification and are uremic toxins that inhibit nitric oxide (NO) production and play multifunctional roles in many human diseases. Both ADMA and SDMA have emerged as strong predictors of cardiovascular events and death in a range of illnesses. Major progress has been made in research on ADMA-lowering therapies in animal studies; however, further studies are required to fill the translational gap between animal models and clinical trials in order to treat human diseases related to elevated ADMA/SDMA levels. Here, we review the reported impacts of ADMA and SDMA on human health and disease, focusing on the synthesis and metabolism of ADMA and SDMA; the pathophysiological roles of these dimethylarginines; clinical conditions and animal models associated with elevated ADMA and SDMA levels; and potential therapies against ADMA and SDMA. There is currently no specific pharmacological therapy for lowering the levels and counteracting the deleterious effects of ADMA and SDMA. A better understanding of the mechanisms underlying the impact of ADMA and SDMA on a wide range of human diseases is essential to the development of specific therapies against diseases related to ADMA and SDMA.

Targeting on Asymmetric Dimethylarginine-Related Nitric Oxide-Reactive Oxygen Species Imbalance to Reprogram the Development of Hypertension

Adult-onset diseases, including hypertension, can originate from early life, known as the developmental origins of health and disease (DOHaD). Because the developing kidney is vulnerable to early-life insults, renal programming is considered key in the developmental programming of hypertension. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide (NO) synthase inhibitor, can regulate the NO–reactive oxygen species (ROS) balance, and is involved in the development of hypertension. Reprogramming interventions aimed at NO-ROS balance can be protective in both genetic and developmentally programmed hypertension. Here we review several emergent themes of the DOHaD approach regarding the impact of ADMA-related NO-ROS imbalance on programmed hypertension. We focus on the kidney in the following areas: mechanistic insights to interpret programmed hypertension; the impact of ADMA-related NO-ROS imbalance in both genetic and acquired animal models of hypertension; alterations of the renal transcriptome in response to ADMA in the developing kidney; and reprogramming strategies targeting ADMA-related NO-ROS balance to prevent programmed hypertension.

Umbilical cord asymmetric dimethylarginine levels and ultrasound assessment of carotid arteries in neonates born small for gestational age

BACKGROUND

To examine asymmetric dimethylarginine (ADMA) level as an endothelial function parameter in addition to ultrasonographic evaluation of carotid arteries in babies born small for gestational age (SGA).

METHODS

Twenty-six neonates born SGA and 34 appropriate for gestational age (AGA) controls were included in the study. The serum levels of ADMA were measured. Intima-media thickness (cIMT) and resistive index (cRI) of the both carotid arteries were determined by ultrasonography.

RESULTS

The mean ADMA level was higher in SGA neonates compared to AGAs (16 267.7 ± 6050 versus 12 810.2 ± 3302 ng/L; p = 0.01). The mean cIMT (0.34 ± 0.02 versus 0.31 ± 0.03 mm; p = 0.001) and cRI (0.66 ± 0.07 versus 0.61 ± 0.04, p = 0.003) were also higher in SGAs. Serum ADMA levels were positively correlated to the mean cIMT (r = 0.41, p = 0.001). Although there was a weak correlation between cIMT and mean cRI (r = 0.26, p = 0.04), no correlation was found between ADMA and mean cRI (r = 0.17, p = 0.18).

CONCLUSIONS

Neonates born SGA have elevated cord blood ADMA level in addition to thicker IMT and higher RI of carotid arteries at birth. ADMA was correlated to cIMT, suggesting that higher ADMA levels might influence vascular health in later life in these neonates.

Maternal N-acetylcysteine therapy regulates hydrogen sulfide-generating pathway and prevents programmed hypertension in male offspring exposed to prenatal dexamethasone and postnatal high-fat diet

Nitric oxide (NO) and hydrogen sulfide (H2S) pathways are involved in the development of hypertension, a condition that can originate from early life. We examined whether asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor)/NO and H2S generating pathway contributed to programmed hypertension in offspring exposed to prenatal dexamethasone (DEX) and postnatal high-fat (HF) and whether N-acetylcysteine (NAC) therapy prevented this process. We examined 16-week-old male rat offspring from five groups: control, DEX (0.1 mg/kg i.p. from gestational day 16-22), HF (58% high-fat diet from weaning to 4 months of age), DEX+HF, and NAC (1% in drinking water during lactation). Prenatal DEX and postnatal HF diet synergistically induced programmed hypertension in adult offspring, which was prevented by maternal NAC therapy. We attributed the protective effects of NAC on two-hit induced programmed hypertension to the reduction of plasma ADMA, restoration of plasma l-arginine-to-ADMA ratio, upregulation of gene expression of H2S-generating enzymes, restoration of renal 3-mercaptopyruvate sulphurtransferase (3MST) protein levels and activity, induction of plasma glutathione level, and reduction of oxidative stress. Manipulation of the ADMA-NO and H2S-generating pathways by maternal NAC therapy may be a potential approach to prevent programmed hypertension induced by two-hit insults.

Increased carotid artery intima-media thickness and myeloperoxidase level in children with newly diagnosed juvenile idiopathic arthritis

Introduction

Juvenile idiopathic arthritis (JIA) is a frequent childhood rheumatic disease characterized by chronic inflammation. The latter has been related to impairment of arterial functional-structural properties, atherogenesis and later cardiovascular events. The objective of this study was to examine intima-media thickness (IMT) and the parameters of arterial stiffness in children with JIA at diagnosis and their correlation with JIA subtype and markers of inflammation and atherosclerosis.

Methods

Thirty-nine newly diagnosed patients with JIA (26 girls; mean age, 13.2 ± 2.6 years) and 27 healthy controls (9 girls; mean age, 13.6 ± 3.4 years) were included in the study. Twelve patients had oligoarthritis, fifteen had extended oligoarthritis and twelve had rheumatoid factor–negative polyarthritis. IMT of the common carotid artery was determined by ultrasonography, carotid-femoral pulse wave velocity (cfPWV) and augmentation index adjusted to a heart rate of 75 beats/min (AIx@75) were determined by applanation tonometry. The serum levels of atherosclerosis-related biomarkers, such as asymmetric dimethylarginine (ADMA), myeloperoxidase (MPO) and adiponectin, were measured by enzyme-linked immunosorbent assay.

Results

Mean IMT (0.46 ± 0.04 vs. 0.42 ± 0.04 mm; p = 0.0003) and MPO concentration (115.2 [95 % confidence interval {95 % CI}, 97.4–136.3] vs. 57.6 [95 % CI, 47.1–70.3] ng/ml; p < 0.0001) were higher in the patients with JIA than in the control subjects. The cfPWV, AIx@75 and serum ADMA and adiponectin levels did not significantly differ between the groups and JIA subtypes. Serum adiponectin level correlated negatively with AIx@75 in patients with JIA (r = −0.38; p < 0.05).

Conclusions

Patients with JIA have increased mean IMT and elevated MPO levels at early stages of the disease. AIx@75 was inversely independently associated with adiponectin level in the patients, suggesting that lower adiponectin levels might influence arterial subclinical stiffening in patients with newly diagnosed JIA.

Nitrergic system and plasmatic methylarginines: Evidence of their role in the perinatal programming of cardiovascular diseases

Atherosclerosis, in turn preceded by endothelial dysfunction, underlies a series of important cardiovascular diseases. Reduced bioavailability of endothelial nitric oxide, by increasing vascular tone and promoting platelet aggregation, leukocyte adhesion, and smooth muscle cell proliferation, plays a key role in the onset of the majority of cardiovascular diseases. In addition, high blood levels of asymmetric dimethylarginine, a potent inhibitor of nitric oxide synthesis, are associated with future development of adverse cardiovascular events and cardiac death. Recent reports have demonstrated that another methylarginine, i.e., symmetric dimethylarginine, is also involved in the onset of endothelial dysfunction and hypertension. Almost a decade ago, prematurity at birth and intrauterine growth retardation were first associated with a potential negative influence on the cardiovascular apparatus, thus constituting risk factors or leading to early onset of cardiovascular diseases. This condition is referred to as cardiovascular perinatal programming. Accordingly, cardiovascular morbidity and mortality are higher among former preterm adults than in those born at term. The aim of this paper was to undertake a comprehensive literature review focusing on cellular and biochemical mechanisms resulting in both reduced nitric oxide bioavailability and increased methylarginine levels in subjects born preterm. Evidence of the involvement of these compounds in the perinatal programming of cardiovascular risk are also discussed.

Plasma levels of dimethylarginines in preterm very low birth weight neonates: its relation with perinatal factors and short-term outcome

Endogenously produced inhibitors of nitric oxide (NO) synthase, in particular asymmetric dimethylarginine (ADMA), are currently considered of importance in various disease states characterized by reduced NO availability. We investigated the association between plasma levels of ADMA, symmetric dimethylarginine (SDMA), l-arginine, and citrulline and perinatal factors and outcome in 130 preterm (gestational age ≤30 weeks) very low birth weight (VLBW, <1500 g) infants. Plasma samples were collected 6–12 h after birth. We did not find significant correlations between ADMA, SDMA, l-arginine, and citrulline levels and gestational age or birth weight. However, the arginine:ADMA ratio (AAR, a better indicator of NO availability than either arginine or ADMA separately) was positively correlated with gestational age. ADMA and arginine levels were not significantly different between males and females but males showed a negative correlation between ADMA levels and gestational age. Perinatal factors such as preeclampsia, chrorioamnionitis, prolonged rupture of membranes, or form of delivery did not significantly alter dimethylarginine levels or AAR. In contrast, the AAR was significantly reduced in the infants with respiratory distress, mechanical ventilation, and systemic hypotension Therefore, our data suggest that altered NO availability may play a role in the respiratory and cardiovascular adaptation in preterm VLBW infants.

Metformin reduces asymmetric dimethylarginine and prevents hypertension in spontaneously hypertensive rats

Elevated asymmetric dimethylarginine (ADMA) levels and nitric oxide (NO) deficiency are associated with the development of hypertension. Metformin, an antidiabetic agent, is a structural analog of ADMA. We examined whether metformin can prevent the development of hypertension in spontaneously hypertensive rats (SHRs) by restoration of ADMA-NO balance. SHRs and control normotensive Wistar-Kyoto (WKY) rats were assigned to 4 groups (N = 8 for each group): untreated SHRs and WKY rats, metformin-treated SHRs and WKY rats. Metformin-treated rats received metformin 500 mg/kg per day via oral gavage for 8 weeks. All rats were sacrificed at the age of 12 weeks. We found an increase in the blood pressure of SHRs was prevented by metformin. ADMA levels in the plasma and lung were elevated in SHRs, which metformin prevented. Lung dimethylarginine dimethylaminohydrolase (DDAH, ADMA-metabolizing enzyme) activity was lower in SHRs than WKY rats. Next, metformin had no effect on protein arginine methyltransferase 1 (ADMA-synthesizing enzyme), DDAH-1, DDAH-2, NO synthase enzymes, and DDAH activity in the kidney. Moreover, metformin increased the levels of NO in kidney. Conclusively, the observed antihypertensive effect of metformin in SHRs is because of the restoration of the ADMA-NO pathway. Our findings support the consideration of metformin as an antihypertensive agent for diabetic patients with prehypertension.

Maternal citrulline supplementation prevents prenatal N(G)-nitro-L-arginine-methyl ester (L-NAME)-induced programmed hypertension in rats

Nitric oxide (NO) deficiency induced by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine-methyl ester (L-NAME) resulted in hypertension. L-citrulline (CIT) can be converted to L-arginine to generate NO. We examined whether maternal CIT supplementation can prevent L-NAME-induced programmed hypertension. Pregnant Sprague-Dawley rats were assigned to four groups: control, L-NAME, control + citrulline (CIT), and L-NAME + citrulline (L-NAME+CIT). Pregnant rats received L-NAME administration at 60 mg/kg/day subcutaneously during pregnancy alone or with additional 0.25% l-citrulline solution in drinking water during the whole period of pregnancy and lactation. Male offspring were sacrificed at 12 wk of age. L-NAME exposure during pregnancy induces hypertension in the 12-wk-old offspring. Maternal CIT therapy prevented L-NAME-induced programmed hypertension, which was associated with a decreased asymmetric dimethylarginine (ADMA) concentration and an increased L-arginine-to-ADMA ratio in the kidney, increased urinary cGMP levels, and decreased renal protein levels of type 3 sodium hydrogen exchanger (NHE3). Together, our data suggest that the beneficial effects of CIT supplementation are attributed to its ability to increase NO level in the kidney and inhibition of NHE3 expression. Our results suggest that supplementing CIT in pregnant women with NO deficiency can improve fetal development and prevent programmed hypertension.

Asymmetric dimethylarginine levels in children with β-thalassemia and their correlations to tricuspid regurgitant jet velocity

BACKGROUND

Pulmonary hypertension (PHT) may be the leading cause of death in β-thalassemia patients; however, its pathophysiologic mechanisms are still unclear. Recent studies indicate that asymmetric dimethylarginine (ADMA) plays a role in the initiation and progression of a variety of diseases, especially the cardiovascular system. The aim of this study is to assess the levels of ADMA in children with β-thalassemia and their correlations with tricuspid regurgitant jet velocity.

PROCEDURES

This study was carried out on 30 children with β-thalassemia major and 30 healthy children served as a control group. Both groups underwent the following investigations: Blood sampling for CBC, LDH, serum ferritin, reticulocytic count, serum bilirubin, AST, ALT, in addition to plasma levels of ADMA. Doppler echocardiography was done for thalassemic group. Patients with tricuspid regurgitant jet velocity (TRV ≥ 2.5 m/sec) were considered risky for PHT.

RESULTS

Plasma ADMA levels were significantly higher in patients with β-thalassemia than control group with a mean value 0.91 ± 0.14 and 0.62 ± 0.10 µmol/L respectively (P = 0.001). There was a significant positive correlation between plasma ADMA levels and tricuspid regurgitant jet velocity. The prevalence of elevated tricuspid regurgitant jet velocity (TRV ≥ 2.5 m/sec) in patients with thalassemia was 33.3%, with a significant increase of elevated TVR (≥ 2.5 m/sec) in patients with thalassemia with splenectomy than in patients without splenectomy.

CONCLUSION

High plasma ADMA levels may be implicated in the pathogenesis of PHT in children with β-thalassemia.

Asymmetric and symmetric dimethylarginine are associated with coronary artery lesions in Kawasaki disease

OBJECTIVE

To determine whether 3 biomarkers, L-arginine, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA), can predict outcomes in patients with Kawasaki disease (KD).

STUDY DESIGN

Plasma levels of L-arginine, ADMA, and SDMA were measured in 39 patients with KD and 27 febrile control patients.

RESULTS

Plasma L-arginine, ADMA, and SDMA levels were lower in patients with KD than in control patients before treatment with intravenous immunoglobulin (IVIG; P=.027, P<.001, and P<.001, respectively). After treatment with IVIG, L-arginine, ADMA, L-arginine/ADMA ratios, and arginine methylation ([ADMA+SDMA]/L-arginine) increased significantly (P<.001, P=.001, P=.014, and P=.001, respectively). Compared with control patients, persistent lower SDMA and higher ADMA/SDMA ratios existed in patients with KD. Furthermore, a lesser magnitude of change in terms of L-arginine and ADMA/SDMA ratios after IVIG treatment was associated with the formation of coronary dilation (P=.025, and .029, respectively).

CONCLUSION

Levels of L-arginine, ADMA, and SDMA appear to be associated with KD. Lower L-arginine levels and ADMA/SDMA after treatment with IVIG was associated with coronary artery abnormalities patients with KD.

Restoration of asymmetric dimethylarginine-nitric oxide balance to prevent the development of hypertension

Despite the use of extensive antihypertensive therapy in patients with hypertension, little attention has been paid to early identification and intervention of individuals at risk for developing hypertension. The imbalance between nitric oxide (NO) and reactive oxygen species (ROS) resulting in oxidative stress has been implicated in the pathophysiology of hypertension. NO deficiency can precede the development of hypertension. Asymmetric dimethylarginine (ADMA) can inhibit nitric oxide synthase (NOS) and regulate local NO/ROS balance. Emerging evidence supports the hypothesis that ADMA-induced NO–ROS imbalance is involved in the development and progression of hypertension. Thus, this review summarizes recent experimental approaches to restore ADMA–NO balance in order to prevent the development of hypertension. Since hypertension might originate in early life, we also discuss the putative role of the ADMA–NO pathway in programmed hypertension. Better understanding of manipulations of the ADMA–NO pathway prior to hypertension in favor of NO will pave the way for the development of more effective medicine for the treatment prehypertension and programmed hypertension. However, more studies are needed to confirm the clinical benefit of these interventions.

Renoprotective effects of melatonin in young spontaneously hypertensive rats with L-NAME

BACKGROUND

Nitric oxide (NO) deficiency occurs in humans and animals with hypertension and chronic kidney disease (CKD). An inhibitor of NO synthase, N(G)-nitro-l-arginine methyl ester (L-NAME) exacerbates kidney damage in the adult spontaneously hypertensive rat (SHR). We examined whether L-NAME exacerbated hypertensive nephrosclerosis in young SHRs and whether melatonin protects SHRs against kidney damage by restoration of the asymmetric dimethylarginine (ADMA)-NO pathway.

METHODS

Rats aged 4 weeks were randomly assigned into three groups (n = 10 for each group): Group 1 (control), SHRs without treatment; Group 2 (L-NAME), SHRs received L-NAME (80 mg/L) in drinking water; and Group 3 (L-NAME + melatonin), SHRs received L-NAME (80 mg/L) and 0.01% melatonin in drinking water. All rats were sacrificed at 10 weeks of age.

RESULTS

L-NAME exacerbates the elevation of blood pressure, renal dysfunction, and glomerular sclerosis in young SHRs. L-NAME induced an increase of ADMA and a decrease of arginine-to-ADMA ratio in the SHR kidney. Melatonin therapy prevented L-NAME-exacerbated hypertension and nephrosclerosis in young SHRs. In addition, melatonin restored L-NAME-induced reduction of dimethylarginine dimethylaminohydrolase (DDAH; ADMA-metabolizing enzymes) activity in the SHR kidney. Next, melatonin decreased renal ADMA concentrations, increased renal arginine-to-ADMA ratio, and restored NO production in L-NAME-treated young SHRs. Moreover, melatonin reduced the degree of oxidative damaged DNA product, 8-hydroxydeoxyguanosine immunostaining in L-NAME-treated SHR kidney.

CONCLUSION

Our results indicated that L-NAME/SHR is a useful model for hypertensive nephrosclerosis in young rats. The blood pressure-lowering and renoprotective effects of melatonin is due to increases of DDAH activity, decreases of ADMA, and reduction of oxidative stress in L-NAME-treated SHR kidney. Specific therapy targeting the DDAH-ADMA pathway may be a promising approach to slowing chronic kidney disease progression in children.

Is asymmetric dimethylarginine associated with being born small and large for gestational age?

Low and high birth weights have been linked to increased susceptibility to cardiovascular and metabolic alterations. However, the natural history of cardiometabolic disturbances in children born small (SGA) and large (LGA) for gestational age is still unclear and no reliable biomarker of cardiovascular risk has definitively been identified in these subjects. Interestingly, asymmetric dimethylarginine (ADMA), antagonist of nitric oxide (NO) production, has been recognized as novel cardiovascular marker able to identify subjects at higher risk of health disturbances. Despite the well-described role of ADMA as a predictor of degenerative disease in adults, its potential application in pediatrics, and specifically in SGA and LGA children, has not been explored as only few data in preterm infants and SGA newborns are available. Therefore, we investigated potential alterations in circulating ADMA and NO levels in SGA and LGA children compared with those born appropriate (AGA) for gestational age. Of note, ADMA was significantly higher in SGA and LGA children than AGA peers. Intriguingly, SGA and LGA categories as well as insulin resistance were independently related to ADMA. Our observations lead to the intriguing hypothesis that ADMA could be involved in the development of cardiometabolic alterations in SGA and LGA children already during the prepubertal age.

Melatonin therapy prevents programmed hypertension and nitric oxide deficiency in offspring exposed to maternal caloric restriction

Nitric oxide (NO) deficiency is involved in the development of hypertension, a condition that can originate early in life. We examined whether NO deficiency contributed to programmed hypertension in offspring from mothers with calorie-restricted diets and whether melatonin therapy prevented this process. We examined 3-month-old male rat offspring from four maternal groups: untreated controls, 50% calorie-restricted (CR) rats, controls treated with melatonin (0.01% in drinking water), and CR rats treated with melatonin (CR + M). The effect of melatonin on nephrogenesis was analyzed using next-generation sequencing. The CR group developed hypertension associated with elevated plasma asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor), decreased L-arginine, decreased L-arginine-to-ADMA ratio (AAR), and decreased renal NO production. Maternal melatonin treatment prevented these effects. Melatonin prevented CR-induced renin and prorenin receptor expression. Renal angiotensin-converting enzyme 2 protein levels in the M and CR + M groups were also significantly increased by melatonin therapy. Maternal melatonin therapy had long-term epigenetic effects on global gene expression in the kidneys of offspring. Conclusively, we attributed these protective effects of melatonin on CR-induced programmed hypertension to the reduction of plasma ADMA, restoration of plasma AAR, increase of renal NO level, alteration of renin-angiotensin system, and epigenetic changes in numerous genes.

Maternal citrulline supplementation prevents prenatal dexamethasone-induced programmed hypertension

Glucocorticoids are administered to premature infants to accelerate pulmonary maturation. In experimental model, prenatal dexamethasone (DEX) results in reduced nephron number and adulthood hypertension. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), can cause oxidative stress and is involved in the development of hypertension. L-citrulline can be converted to l-arginine (the substrate for NOS) in the body. Thus we intended to determine if maternal L-citrulline therapy can prevent prenatal DEX-induced programmed hypertension by restoration ADMA/nitric oxide (NO) balance, alterations of renin-angiotensin system (RAS) and sodium transporters, and epigenetic regulation by histone deacetylases (HDACs). Male offspring were assigned to four groups: control, pregnancy rats received intraperitoneal DEX (0.2 mg/kg body weight) daily on gestational days 15 and 16 (DEX), pregnancy rats received 0.25% L-citrulline in drinking water during the entire pregnancy and lactation period (CIT), and DEX + CIT. We found DEX group developed hypertension at 16 weeks of age, which was prevented by maternal L-citrulline therapy. Prenatal DEX exposure increased plasma ADMA concentrations and reduced renal NO production. However, L-citrulline reduced plasma ADMA level and increased renal level of NO in DEX + CIT group. Next, prenatal DEX-induced programmed hypertension is related to increased mRNA expression of angiotensin and angiotensin II type 1 receptor, and class I HDACs in the kidney. Prenatal DEX exposure increased renal protein abundance of Na(+)/Cl(-) cotransporter (NCC), which was prevented by L-citrulline therapy. The beneficial effects of L-citrulline therapy include restoration of ADMA/NO balance and alteration of NCC, to prevent the prenatal DEX-induced programmed hypertension.

Increased circulatory asymmetric dimethylarginine and multiple organ failure: bile duct ligation in rat as a model

Bile duct ligation (BDL)-treated rats exhibit cholestasis, increased systemic oxidative stress, and liver fibrosis, which ultimately lead to liver cirrhosis. Asymmetric dimethylarginine (ADMA) is a competitive inhibitor of nitric oxide synthase that can decrease the synthesis of nitric oxide. BDL rats have higher plasma and hepatic ADMA levels, which may be due to increased hepatic protein arginine methyltransferase-1 and decreased dimethylarginine dimethylaminohydrolase expression. BDL rats also exhibit renal and brain damage characterized by increased tissue ADMA concentrations. The increased plasma ADMA levels and multiple organ damages seen here are also observed following multiple organ failures associated with critical illness. This review discusses the dysregulation of ADMA in major organs in BDL rats and the role of increased ADMA in multiple organ damages.

Evaluation of asymmetric dimethylarginine (ADMA) levels in children with growth hormone deficiency

OBJECTIVE

To investigate serum asymmetric dimethylarginine (ADMA) levels in children with isolated growth hormone deficiency (GHD) and to determine the effect of GH replacement therapy on these levels.

METHODS

31 patients diagnosed with isolated GHD and 29 age-and sex-matched healthy children were enrolled in the study. Height, weight and waist circumference were measured in all subjects. Fasting serum insulin-like growth factor-1 (IGF-1), IGF binding protein-3, glucose, insulin and lipid levels were evaluated. Serum ADMA levels were assessed using the enzyme-linked immunosorbent assay technique. The same evaluations were repeated on the 3rd and 6th months of treatment in 28 of the GHD cases.

RESULTS

There were no significant differences in ADMA levels between the patient and control groups [0.513±0.130 (0.291-0.820) µmol/L vs. 0.573±0.199 (0.241-1.049) µmol/L]. There was a positive correlation between serum ADMA and HbA1c levels in the control group. In the GHD cases, ADMA levels negatively correlated with high-density lipoprotein levels and positively correlated with low-density lipoprotein levels. There was also a significant increase in ADMA levels in patients receiving GH therapy compared to pre-treatment levels [serum ADMA level, 1.075±0.133 (0.796-1.303) µmol/L at the 3rd month and 0.923±0.121 (0.695-1.159) µmol/L at the 6th month of treatment]. There was a negative correlation between ADMA levels and homeostasis model assessment of insulin resistance values at the 6th month evaluation. There were no relationships between ADMA levels and age, sex, or pubertal state either before or during the treatment.

CONCLUSION

Serum ADMA levels were found to be similar in patients with GHD and in healthy children. However, serum ADMA levels showed a significant increase in GHD patients following GH replacement therapy.

Melatonin attenuates prenatal dexamethasone-induced blood pressure increase in a rat model

Although antenatal corticosteroid is recommended to accelerate fetal lung maturation, prenatal dexamethasone exposure results in hypertension in the adult offspring. Since melatonin is a potent antioxidant and has been known to regulate blood pressure, we examined the beneficial effects of melatonin therapy in preventing prenatal dexamethasone-induced programmed hypertension. Male offspring of Sprague-Dawley rats were assigned to four groups (n = 12/group): control, dexamethasone (DEX), control + melatonin, and DEX + melatonin. Pregnant rats received intraperitoneal dexamethasone (0.1 mg/kg) from gestational day 16 to 22. In the melatonin-treatment groups, rats received 0.01% melatonin in drinking water during their entire pregnancy and lactation. Blood pressure was measured by an indirect tail-cuff method. Gene expression and protein levels were analyzed by real-time quantitative polymerase chain reaction and Western blotting, respectively. At 16 weeks of age, the DEX group developed hypertension, which was partly reversed by maternal melatonin therapy. Reduced nephron numbers due to prenatal dexamethasone exposure were prevented by melatonin therapy. Renal superoxide and NO levels were similar in all groups. Prenatal dexamethasone exposure led to increased mRNA expression of renin and prorenin receptor and up-regulated histone deacetylase (HDAC)-1 expression in the kidneys of 4-month-old offspring. Maternal melatonin therapy augmented renal Mas protein levels in DEX + melatonin group, and increased renal mRNA expression of HDAC-1, HDAC-2, and HDAC-8 in control and DEX offspring. Melatonin attenuated prenatal DEX-induced hypertension by restoring nephron numbers, altering RAS components, and modulating HDACs.

Two different approaches to restore renal nitric oxide and prevent hypertension in young spontaneously hypertensive rats: l-citrulline and nitrate

Nitric oxide (NO) deficiency mediates oxidative stress in the kidney and is involved in the development of hypertension. NO synthesis occurs via 2 pathways: nitric oxide synthase (NOS) dependent and NOS-independent. We tested whether the development of hypertension is prevented by restoration of NO by dietary l-citrulline or nitrate supplementation in young spontaneously hypertensive rats (SHRs). Male SHRs and normotensive Wistar Kyoto control rats (WKYs)s age 4 weeks were assigned to 4 groups: untreated SHRs and WKYs, and SHRs and WKYs that received 0.25% l-citrulline for 8 weeks. In our second series of studies, we replaced l-citrulline with 1 mmol/kg/d sodium nitrate. All rats were sacrificed at age 12 weeks. We found an increase in the blood pressure of SHRs was prevented by dietary supplementation of l-citrulline or nitrate. Both treatments restored NO bioavailability and reduced oxidative stress in SHR kidneys. l-Citrulline therapy reduced levels of l-arginine and asymmetric dimethylarginine (ADMA)-an endogenous inhibitor of NOS-and increased the l-arginine-to-ADMA ratio in SHR kidneys. Nitrate treatment reduced plasma levels of l-arginine and ADMA concurrently in SHRs. Our findings suggest that both NOS-dependent and -independent approaches in the prehypertensive stage toward augmentation of NO can prevent the development of hypertension in young SHRs.

Carotid intima-media thickness and plasma asymmetric dimethylarginine in Mexican children exposed to inorganic arsenic

BACKGROUND

Arsenic exposure is a risk factor for atherosclerosis in adults, but there is little information on arsenic and early risk biomarkers for atherosclerosis in children. Carotid intima-media thickness (cIMT) is an indicator of subclinical atherosclerotic burden that has been associated with plasma asymmetric dimethylarginine (ADMA), a predictor of cardiovascular disease risk.

OBJECTIVES

The aim of this study was to investigate associations of arsenic exposure with cIMT, ADMA, and endothelial adhesion molecules [soluble intercellular cell adhesion molecule-1 (sICAM-1); soluble vascular cell adhesion molecule-1 (sVCAM-1)] in children who had been exposed to environmental inorganic arsenic (iAs).

METHODS

We conducted a cross-sectional study in 199 children 3-14 years of age who were residents of Zimapan, México. We evaluated cIMT using ultrasonography, and plasma lipid profiles by standard methods. We analyzed ADMA, sICAM-1, and sVCAM-1 by ELISA, and measured the concentrations of total speciated arsenic (tAs) in urine using hydride generation cryotrapping atomic absorption spectrometry.

RESULTS

In the multiple linear regression model for cIMT, tAs categories were positively associated with cIMT increase. The estimated cIMT diameter was greater in 35- to 70-ng/mL and > 70-ng/mL groups (0.035 mm and 0.058 mm per 1-ng/mL increase in urinary tAs, respectively), compared with the < 35-ng/mL group. In addition to tAs level, plasma ADMA was a significant predictor of cIMT. In the adjusted regression model, cIMT, percent iAs, and plasma sVCAM-1 were significant predictors of ADMA levels (e.g., 0.419-μmol/L increase in ADMA per 1-mm increase in cIMT).

CONCLUSIONS

Arsenic exposure and plasma ADMA levels were positively associated with cIMT in a population of Mexican children with environmental arsenic exposure through drinking water.

Sex differences of oxidative stress to cholestatic liver and kidney injury in young rats

BACKGROUND

Sexual dimorphism plays a role in the liver and in renal injuries. However, whether sex is a risk factor in bile duct ligation (BDL) in young rats has never been examined.

METHODS

Six male and six female rats treated with BDL were sacrificed 2 weeks after surgery and were designated as BDL-M and BDL-F groups. The other six male and six female rats that received sham ligation were designated as sham-M and sham-F groups. Plasma biochemistry and liver and kidney asymmetric dimethylarginine (ADMA)-related molecules were examined.

RESULTS

Both BDL-M and BDL-F groups had elevated plasma aspartate transaminase (AST), alanine transaminase (ALT), bilirubin, and transforming growth factor-β1 levels. The BDL-F group had lower plasma AST and ALT levels than the BDL-M group. The BDL-M and BDL-F groups had elevated plasma ADMA levels. The cationic amino acid transporter 1 (CAT1) level was increased in the BDL-F group as compared to the sham-F group, whereas the CAT2 level was reduced in the both BDL-M and BDL-F groups.

CONCLUSION

We found that young male rats were prone to higher degrees of biochemical liver and kidney injury to cholestasis. Sex differences in modulation of oxidative stress markers, such as ADMA, may play a role. Our results support careful monitoring and optimal treatment of cholestatic disease, especially in young male patients.

Roles of nitric oxide and asymmetric dimethylarginine in pregnancy and fetal programming

Nitric oxide (NO) regulates placental blood flow and actively participates in trophoblast invasion and placental development. Asymmetric dimethylarginine (ADMA) can inhibit NO synthase, which generates NO. ADMA has been associated with uterine artery flow disturbances such as preeclampsia. Substantial experimental evidence has reliably supported the hypothesis that an adverse in utero environment plays a role in postnatal physiological and pathophysiological programming. Growing evidence suggests that the placental nitrergic system is involved in epigenetic fetal programming. In this review, we discuss the roles of NO and ADMA in normal and compromised pregnancies as well as the link between placental insufficiency and epigenetic fetal programming.

Cardiovascular risk in autoimmune disorders: role of asymmetric dimethylarginine

Mounting evidence indicates that cardiovascular events are a main cause of excessive mortality of autoimmune disorders like type I diabetes mellitus and rheumatic diseases. Inflammation and endothelial dysfunction, independent predictors to cardiovascular disease, are hallmarks of autoimmunity. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, can cause or contribute to the inflammatory syndrome and endothelial dysfunction. Recently, elevated ADMA levels have been demonstrated in many autoimmune diseases, suggesting that ADMA might play an important role for the associated manifestations of cardiovascular disease. In the review, we discuss the role of ADMA in the excessive cardiovascular morbidity and mortality associated with autoimmune diseases.

Asymmetric dimethylarginine, endothelial dysfunction and renal disease

l-Arginine (Arg) is oxidized to l-citrulline and nitric oxide (NO) by the action of endothelial nitric oxide synthase (NOS). In contrast, protein-incorporated Arg residues can be methylated with subsequent proteolysis giving rise to methylarginine compounds, such as asymmetric dimethylarginine (ADMA) that competes with Arg for binding to NOS. Most ADMA is degraded by dimethylarginine dimethyaminohydrolase (DDAH), distributed widely throughout the body and regulates ADMA levels and, therefore, NO synthesis. In recent years, several studies have suggested that increased ADMA levels are a marker of atherosclerotic change, and can be used to assess cardiovascular risk, consistent with ADMA being predominantly absorbed by endothelial cells. NO is an important messenger molecule involved in numerous biological processes, and its activity is essential to understand both pathogenic and therapeutic mechanisms in kidney disease and renal transplantation. NO production is reduced in renal patients because of their elevated ADMA levels with associated reduced DDAH activity. These factors contribute to endothelial dysfunction, oxidative stress and the progression of renal damage, but there are treatments that may effectively reduce ADMA levels in patients with kidney disease. Available data on ADMA levels in controls and renal patients, both in adults and children, also are summarized in this review.

The combined ratios of L-arginine and asymmetric and symmetric dimethylarginine as biomarkers in spontaneously hypertensive rats

Hypertension and hypertensive end-organ damage have been associated with decreased nitric oxide (NO) bioavailability. Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) both can inhibit NO availability by competition with L-arginine (L-Arg). However, whether a combined analysis of these 3 parameters can serve as an ideal biomarker of hypertension remains unclear. We measured the plasma and renal levels of L-Arg, ADMA, and SDMA in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) control rats at 3 stages: 4 weeks old (prehypertensive), 12 weeks old (hypertensive), and 24 weeks old (end-organ damage). The plasma and renal L-Arg/ADMA ratio (AAR) and the ADMA/SDMA ratio (ASR) were computed for all 3 age stages. Our results revealed an ADMA level increase, and an AAR decrease in plasma and kidneys may develop early on, even before the onset of hypertension in 4-week-old SHRs. The renal ADMA level and AAR were restored in SHRs at 24 weeks of age, which might protect SHRs against kidney injury. We found that the plasma AAR is superior to the levels of L-Arg and ADMA in plasma, and it predicted blood pressure and urinary NOx levels. Renal AAR is a strong independent marker of renal dimethylarginine dimethylaminohydrolase (DDAH) activity. The plasma ASR was correlated strongly to blood pressure. However, renal DDAH activity was related to the renal ASR but not the plasma ASR. In conclusion, the AAR and ASR may serve as better markers for disease activity and progression than each individual parameter. Clinical use of these ratios to elucidate the role of ADMA in hypertension awaits further validation.