Determination of asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, in umbilical blood

Increased Oxidative Stress and Decreased Citrulline in Blood Associated with Severe Novel Coronavirus Pneumonia in Adult Patients

This study investigated the correlation between oxidative stress and blood amino acids associated with nitric oxide metabolism in adult patients with coronavirus disease (COVID-19) pneumonia. Clinical data and serum samples were prospectively collected from 100 adult patients hospitalized for COVID-19 between July 2020 and August 2021. Patients with COVID-19 were categorized into three groups for analysis based on lung infiltrates, oxygen inhalation upon admission, and the initiation of oxygen therapy after admission. Blood data, oxidative stress-related biomarkers, and serum amino acid levels upon admission were compared in these groups. Patients with lung infiltrations requiring oxygen therapy upon admission or starting oxygen post-admission exhibited higher serum levels of hydroperoxides and lower levels of citrulline compared to the control group. No remarkable differences were observed in nitrite/nitrate, asymmetric dimethylarginine, and arginine levels. Serum citrulline levels correlated significantly with serum lactate dehydrogenase and C-reactive protein levels. A significant negative correlation was found between serum levels of citrulline and hydroperoxides. Levels of hydroperoxides decreased, and citrulline levels increased during the recovery period compared to admission. Patients with COVID-19 with extensive pneumonia or poor oxygenation showed increased oxidative stress and reduced citrulline levels in the blood compared to those with fewer pulmonary complications. These findings suggest that combined oxidative stress and abnormal citrulline metabolism may play a role in the pathogenesis of COVID-19 pneumonia.

Association of Umbilical Cord Serum Oxidative Stress Markers, ADMA and Adiponectin with Adverse Fetal Outcomes in Hypertensive Disorders of Pregnancy

BACKGROUND

Limited studies are available on fetal oxidative stress and endothelial dysfunction and their association with adverse fetal outcomes in hypertensive disorders of pregnancy (HDP). Method: Umbilical cord blood samples were collected at delivery from 134 pregnant women with HDP and 59 controls. Markers of oxidative stress, endothelial dysfunction and inflammation and adipokines were analyzed. Results were correlated with adverse fetal outcomes. Results: Malondialdehyde, total antioxidant status(TAS), ADMA and hsCRP levels were increased in late and early onset preeclampsia. Adiponectin levels were decreased in early onset preeclampsia. High ADMA levels were positively associated with preterm births and fetal mortality and high TAS, protein carbonyl content(PC), ADMA and low adiponectin levels were positively associated with low birth weight babies. Conclusion: Fetal systemic oxidative stress, endothelial dysfunction and inflammation were altered in early and late onset preeclampsia. High TAS, PC and ADMA levels and low adiponectin levels were positively associated with adverse fetal outcomes in HDP.

Perinatal Oxidative Stress and Kidney Health: Bridging the Gap between Animal Models and Clinical Reality

Oxidative stress arises when the generation of reactive oxygen species or reactive nitrogen species overwhelms antioxidant systems. Developing kidneys are vulnerable to oxidative stress, resulting in adult kidney disease. Oxidative stress in fetuses and neonates can be evaluated by assessing various biomarkers. Using animal models, our knowledge of oxidative-stress-related renal programming, the molecular mechanisms underlying renal programming, and preventive interventions to avert kidney disease has grown enormously. This comprehensive review provides an overview of the impact of perinatal oxidative stress on renal programming, the implications of antioxidant strategies on the prevention of kidney disease, and the gap between animal models and clinical reality.

Reactive Oxygen Species and Antioxidative Defense in Chronic Obstructive Pulmonary Disease

The respiratory system is continuously exposed to endogenous and exogenous oxidants. Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation of the airways, leading to the destruction of lung parenchyma (emphysema) and declining pulmonary function. It is increasingly obvious that reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the progression and amplification of the inflammatory responses related to this disease. First, we described the association between cigarette smoking, the most representative exogenous oxidant, and COPD and then presented the multiple pathophysiological aspects of ROS and antioxidative defense systems in the development and progression of COPD. Second, the relationship between nitric oxide system (endothelial) dysfunction and oxidative stress has been discussed. Third, we have provided data on the use of these biomarkers in the pathogenetic mechanisms involved in COPD and its progression and presented an overview of oxidative stress biomarkers having clinical applications in respiratory medicine, including those in exhaled breath, as per recent observations. Finally, we explained the findings of recent clinical and experimental studies evaluating the efficacy of antioxidative interventions for COPD. Future breakthroughs in antioxidative therapy may provide a promising therapeutic strategy for the prevention and treatment of COPD.

Relation of asymmetric dimethylarginine with pulmonary morbidities in neonatal respiratory distress syndrome

BACKGROUND

Asymmetric Dimethyl Arginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS) is important in different diseases characterized by decreased nitric oxide (NO) availability. We aimed to assess the serum ADMA level in preterm infants suffering from respiratory distress syndrome (RDS) and its relationship with pulmonary outcomes.

METHODS

This prospective study included 50 preterm neonates suffering from RDS aging≤32 weeks and weighing≤1500  gm. Serum ADMA levels were estimated in the 1st and 28th day of life by ELISA, and its correlation with surfactant requirement, duration of ventilation, and development of BPD was assessed.

RESULTS

Fifty preterm infants with RDS were included, 30 infants were treated with surfactant within 12 hours after birth, the 1stday ADMA level was higher significantly in infants who required surfactant treatment than infants without surfactant treatment, At 36 weeks postmenstrual age, 16 infants were diagnosed with BPD, the 28th day ADMA level was significantly higher in infants with BPD than others without BPD. 1st-day ADMA level was significantly correlated with days on mechanical ventilation but there were no significant correlations between 1st day ADMA and days on CPAP and days on supplemental O2.

CONCLUSION

Elevated serum ADMA level in preterm neonates with RDS estimated in the 1st and 28th day of life is a good predictor for pulmonary morbidities such as surfactant requirement, duration of mechanical ventilation, and development of BPD.

The role and mechanism of asymmetric dimethylarginine in fetal growth restriction via interference with endothelial function and angiogenesis

PURPOSE

Fetal growth restriction (FGR) is a high-risk pregnancy, and placental dysfunction is the main cause of FGR. The upregulation of asymmetric dimethylarginine (ADMA) is linked to FGR pathology, but the mechanism needs to be investigated.

METHODS

The levels of ADMA and other related molecules were measured in human biological samples. We further used human umbilical vein endothelial cells (HUVECs) to reveal the mechanism of ADMA-induced FGR in vitro.

RESULTS

Compared with the control group, FGR patients had higher placental resistance, and ADMA levels were increased in the maternal blood, cord blood, and placenta; additionally, nitric oxide (NO) production decreased, accompanied by a decreased expression of endogenous NO synthase (eNOS). The expression of vascular growth factor (VEGF) and placental growth factor (PLGF) in the maternal blood during the third trimester and umbilical cord of the FGR group was lower than the control group. The PLGF levels in the placentas of the FGR group were also reduced, while the expression of soluble fms-like tyrosine kinase-1 (sFlt-1) increased. In in vitro cell experiments, NO production was obviously lower when the cells were exposed to 100 μM of ADMA, with no difference in eNOS expression. There was a dose-dependent decrease in PLGF expression with increasing doses of ADMA, and the levels of sFlt-1 increased. Moreover, we confirmed that tube formation in HUVECs was lower after ADMA treatment compared with the control group.

CONCLUSION

The accumulation of ADMA during pregnancy has an adverse effect on fetal development via interference with placental endothelial function and angiogenesis.

The role of gasotransmitters in neonatal physiology

The gasotransmitters, nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO), are endogenously-produced volatile molecules that perform signaling functions throughout the body. In biological tissues, these small, lipid-permeable molecules exist in free gaseous form for only seconds or less, and thus they are ideal for paracrine signaling that can be controlled rapidly by changes in their rates of production or consumption. In addition, tissue concentrations of the gasotransmitters are influenced by fluctuations in the level of O₂ and reactive oxygen species (ROS). The normal transition from fetus to newborn involves a several-fold increase in tissue O₂ tensions and ROS, and requires rapid morphological and functional adaptations to the extrauterine environment. This review summarizes the role of gasotransmitters as it pertains to newborn physiology. Particular focus is given to the vasculature, ventilatory, and gastrointestinal systems, each of which uniquely illustrate the function of gasotransmitters in the birth transition and newborn periods. Moreover, given the relative lack of studies on the role that gasotransmitters play in the newborn, particularly that of H₂S and CO, important gaps in knowledge are highlighted throughout the review.

Clinical Presentation of Preeclampsia and the Diagnostic Value of Proteins and Their Methylation Products as Biomarkers in Pregnant Women with Preeclampsia and Their Newborns

Preeclampsia (PE) is a disorder which affects 1-10% of pregnant women worldwide. It is characterised by hypertension and proteinuria in the later stages of gestation and can lead to maternal and perinatal morbidity and mortality. Other than the delivery of the foetus and the removal of the placenta, to date there are no therapeutic approaches to treat or prevent PE. It is thus only possible to reduce PE-related mortality through early detection, careful monitoring, and treatment of the symptoms. For these reasons the search for noninvasive, blood-borne, or urinary biochemical markers that could be used for the screening, presymptomatic diagnosis, and prediction of the development of PE is of great urgency. So far, a number of biomarkers have been proposed for predicting PE, based on pathophysiological observations, but these have mostly proven to be unreliable and inconsistent between different studies. The clinical presentation of PE and data gathered for the biochemical markers placental growth factor (PlGF), soluble Feline McDonough Sarcoma- (fms-) like tyrosine kinase-1 (sFlt-1), asymmetric dimethylarginine (ADMA), and methyl-lysine is being reviewed with the aim of providing both a clinical and biochemical understanding of how these biomarkers might assist in the diagnosis of PE or indicate its severity.

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.

Increased asymmetric dimethylarginine levels in severe transient tachypnea of the newborn

OBJECTIVE

Nitric oxide (NO) is synthesized by NO synthase (NOS), and asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NOS. We aimed to investigate l-arginine and ADMA levels in transient tachypnea of the newborn (TTN) and their relationship with systolic pulmonary artery pressure (PAP) and disease severity.

STUDY DESIGN

Infants born at ⩾35 weeks gestational age with clinical signs and chest X-ray findings consistent with TTN were enrolled; controls were recruited at the same time. l-arginine and ADMA levels were measured at 12 to 24 h (first samples) and at 48 to 72 h (second samples). Systolic PAP was evaluated on the second day. Patients were divided according to the duration of tachypnea and designated as group A (duration ⩽72 h) and group B (duration >72 h).

RESULTS

In the first samples, the ADMA levels were significantly higher in patients with TTN compared with controls (P<0.001). In the second samples, the ADMA levels were significantly higher in group B compared with that in group A (P=0.019). In group A patients, the second ADMA levels were significantly lower compared with that in the first samples (P<0.001), whereas the second ADMA levels remained unchanged compared with the first samples in group B. Systolic PAP values were significantly higher in group B compared with that in group A patients (P=0.033).

CONCLUSION

Increased ADMA concentration may reduce NO synthesis, leading to increased PAP and thus longer duration of tachypnea.

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.

Characteristics of NO cycle coupling with urea cycle in non-hyperammonemic carriers of ornithine transcarbamylase deficiency

Urea cycle deficient patients with prominent hyperammonemic often exhibit abnormal production of nitric oxide (NO), which reduces vascular tone, along with amino acid abnormalities. However, information related to the metabolic changes in heterozygotes of ornithine transcarbamylase deficiency (OTCD) lacking overt hyperammonemia is quite limited. We examined vascular mediators and amino acids in non-hyperammonemic heterozygotes. Twenty-four heterozygous OTCD adult females without hyperammonemic bouts, defined as non-hyperammonemic carriers, were enrolled. We measured blood amino acids constituting urea cycle and nitric oxide (NO) cycle. Blood concentrations of nitrate/nitrite (NOx) as stable NO-metabolites, asymmetric dimethylarginine (ADMA) inhibiting NO synthesis, and endothelin-1 (ET-1) raising vascular tone were also determined. NOx concentrations were significantly lower in non-hyperammonemic carriers (p < 0.01). However, ADMA and ET-1 levels in this group were comparable to those in the age-matched control group. Arginine and citrulline levels were also significantly lower in non-hyperammonemic carriers than in controls (p < 0.01). Of the 24 non-hyperammonemic carriers, 10 often developed headaches. Their daily NOx and arginine levels were significantly lower than those in headache-free carriers (p < 0.05). In three carriers receiving oral l-arginine, blood NOx concentrations were significantly higher. In two of those three, the occurrence of headaches was decreased. These results suggest that NO cycle coupling with the urea cycle is altered substantially even in non-hyperammonemic OTCD carriers, predisposing them to headaches.

Feto-placental nitric oxide, asymmetric dimethylarginine and vascular endothelial growth factor (VEGF) levels and VEGF gene polymorphisms in severe preeclampsia

OBJECTIVE

To measure plasma nitric oxide (NO), asymmetric dimethylarginine (ADMA) and vascular endothelial growth factor (VEGF) levels and VEGF gene polymorphisms in fetal circulation in severe preeclampsia.

METHODS

Cord vessels of singleton gestations complicated with severe preeclampsia 36 weeks or more (n = 31) and controls were sampled upon delivery for analyte measuring. Additionally, DNA was extracted from umbilical vein whole blood to determine the frequency of VEGF gene single nucleotide polymorphisms (SNPs): -2578 A/C, -1498 C/T, -1154 A/G, -634 C/G and +936 C/T. Coefficient correlations between analyte levels and placental and neonatal weight were calculated.

RESULTS

NO plasma levels in umbilical vessels (artery and vein) were significantly higher in preeclampsia cases as compared to controls (4.67 ± 3.0 vs. 0.82 ± 0.90; 4.46 ± 3.0 vs. 0.82 ± 0.99 mmol/L, respectively, p = 0.0001 both). ADMA levels displayed a similar increased trend in both fetal vessels, but this did not reach statistical significance (2.57 ± 1.03 vs. 2.34 ± 0.57; 2.74 ± 0.94 vs. 2.42 ± 0.59 mmol/L, respectively, p > 0.05). VEGF was significantly lower in artery but not in vein in preeclampsia cases (200.48 ± 225.62 vs. 338.61 ± 287.03 pg/mL, p = 0.04). A significant positive correlation was found between NO and ADMA levels (artery and vein) among preeclampsia cases. Overall, the frequency of the studied VEGF gene SNPs did not differ among pre-eclamptic cases and controls; nevertheless, a significant trend toward lower umbilical vein VEGF levels was observed in pre-eclampsia cases in the presence of -2578 CC and -1154 AG genotypes.

CONCLUSION

Near term gestations complicated with severe preeclampsia presented higher NO levels in fetal circulation, which correlated to ADMA and lower artery VEGF values. More research is warranted to confirm that selected VEGF SNPs may be associated with lower umbilical vein VEGF.

Birth by cesarean section is associated with elevated neonatal plasma levels of dimethylarginines

BACKGROUND

This study was undertaken to compare the effects of vaginal delivery and cesarean section on the L-arginine-nitric oxide system by measuring levels of L-arginine, an endogenous nitric oxide synthase antagonist asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA) in the cord blood and postnatally.

METHODS

Plasma samples were obtained from the umbilical vein and artery at birth and from peripheral venous blood on the second postnatal day in 30 full-term newborn infants: 10 born vaginally and 20 born by cesarean section.

RESULTS

After vaginal delivery, ADMA concentration was higher in the umbilical vein than in the umbilical artery (mean 1.06 vs 0.90 µmol/L [P = 0.027]); and ADMA level fell after birth to 0.66 µmol/L on the second postnatal day (P = 0.007 vs umbilical artery). Newborns born by cesarean section had similar ADMA levels in umbilical arterial and venous blood, 1.19 and 1.18 µmol/L, and the ADMA level fell to 0.84 µmol/L by the second postnatal day (P < 0.001). Vaginal birth induced neither significant umbilical venoarterial difference nor a postnatal fall in SDMA. After cesarean section, SDMA was essentially the same in umbilical vein, umbilical artery and postnatal peripheral vein samples. At 2 days of age, both ADMA and SDMA levels stayed higher in infants born by cesarean section than in vaginally born infants.

CONCLUSIONS

ADMA level falls after both vaginal and cesarean birth, whereas SDMA level does not. The higher ADMA level after cesarean birth compared with vaginal birth may contribute to decreased nitric oxide production and bioavailability in neonatal vascular beds.

Asymmetric dimethylarginine in normotensive pregnant women with isolated fetal intrauterine growth restriction: a comparison with preeclamptic women with and without intrauterine growth restriction

OBJECTIVE

The aim of this study was to evaluate maternal asymmetric dimethylarginine (ADMA) levels in pregnancies complicated by isolated fetal intrauterine growth restriction (IUGR), in preeclamptic pregnancies with and without IUGR, and in healthy normotensive pregnant women with proper weight fetuses.

PATIENTS AND METHODS

The study was carried out on 54 normotensive pregnant patients with pregnancy complicated by IUGR, 35 patients with IUGR in the course of preeclampsia, 29 preeclamptic patients with appropriate-for-gestational-age weight infants and 54 healthy normotensive pregnant patients. The ADMA concentrations were evaluated using an ELISA assay.

RESULTS

The preeclamptic women and normotensive patients with pregnancy complicated by isolated IUGR revealed higher levels of maternal serum ADMA. The mean values of maternal serum ADMA were 0.5730 ± 0.1769 μmol/l in the P group, 0.5727 ± 0.1756 μmol/l in the PI group, 0.6129 ± 0.1517 μmol/l in the IUGR group, and 0.5017 ± 0.1116 μmol/l in the control group. The levels of ADMA were additionally higher in the patients with HELLP syndrome and in patients with pregnancy complicated by eclampsia.

CONCLUSIONS

It seems that ADMA is an active agent not only in preeclamptic patients, but also in normotensive pregnant women with isolated fetal IUGR and could be a marker of severity of preeclampsia.

Altered metabolisms of mediators controlling vascular function and enhanced oxidative stress in asymptomatic children with congenital portosystemic venous shunt

Children with congenital portosystemic venous shunt (PSVS) are at risk for developing pulmonary hypertension, irrespective of the severity of portal hypertension or liver damage. Altered metabolisms of nitric oxide (NO) and endothelin-1 (ET-1), which are linked with oxidative stress and control vascular tone, might contribute to the vascular disturbance. This study examined 14 children (aged 1-5 years) with congenital PSVS lacking major liver damage and portal hypertension. Serum levels of nitrite/nitrate (NOx) as stable metabolites of NO, and of asymmetric dimethylarginine (ADMA) as an endogenous NO synthase inhibitor were determined, along with the plasma level of ET-1. Oxidative stress, which might affect the production of such mediators, was also examined using specific urinary and blood markers. The NOx levels were significantly lower in affected children than in the age-matched control group, although ET-1 levels were significantly higher than the control levels. In the affected children, the ADMA levels and ADMA/NOx ratios were higher, respectively, by 30% and 130% and showed significant positive correlations with the shunt ratios. Oxidative stress markers, including plasma thiobarbiturate reactive substances and urinary acrolein-lysine and 8-hydroxy-2'-deoxyguanosine, were significantly higher in affected children than in the control group, consistent with them being subjected to enhanced oxidative stress. These results suggest the presence of altered metabolisms of vascular mediators and enhanced oxidative stress in asymptomatic preschool children with congenital PSVS.

Asymmetric dimethylarginine in the maternal and fetal circulation in preeclampsia

Preeclampsia is a leading cause of intrauterine growth restriction and preterm birth. Endothelial dysfunction is the common final pathway leading to clinical signs of preeclampsia including hypertension and proteinuria. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NOS and induces endothelial dysfunction by reversibly inhibiting NO production from l-arginine. The purpose of this study was to investigate maternal and fetal concentrations of ADMA, l-arginine, and symmetric dimethylarginine (SDMA). Women with preeclampsia (n = 47) and controls (n = 51) who gave birth by cesarean section were included in the study. We analyzed the maternal plasma and umbilical vein and artery plasma. We found that not only maternal concentrations of ADMA and SDMA but also l-arginine were significantly higher in women with preeclampsia than in controls. In fetal samples, only SDMA concentrations were higher in the preeclampsia group than in controls. The median ADMA concentration was three times higher in the fetal circulation than in the maternal circulation, but there was no difference between the preeclampsia group and the control group, and the veno-arterious gradient indicated that the placenta was the source of ADMA.

Sustaining hypercitrullinemia, hypercholesterolemia and augmented oxidative stress in Japanese children with aspartate/glutamate carrier isoform 2-citrin-deficiency even during the silent period

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) shows diverse metabolic abnormalities such as urea cycle dysfunction together with citrullinemia, galactosemia, and suppressed gluconeogenesis. Such abnormalities apparently resolve during the first year of life. However, metabolic profiles of the silent period remain unknown. We analyzed oxidative stress markers and profiles of amino acids, carbohydrates, and lipids in 20 asymptomatic children with aspartate/glutamate carrier isoform 2-citrin-deficiency aged 1-10 years, for whom tests showed normal liver function. Despite normal plasma ammonia levels, the affected children showed higher blood levels of ornithine (p<0.001) and citrulline (p<0.01)--amino acids involved in the urea cycle--than healthy children. Blood levels of nitrite/nitrate, metabolites of nitric oxide (NO), and asymmetric dimethylarginine inhibiting NO production from arginine were not different between these two groups. Blood glucose, galactose, pyruvate, and lactate levels after 4-5h fasting were not different between these groups, but the affected group showed a significantly higher lactate to pyruvate ratio. Low-density and high-density lipoprotein cholesterol levels in the affected group were 1.5 times higher than those in the controls. Plasma oxidized low-density lipoprotein apparently increased in the affected children; their levels of urinary oxidative stress markers such as 8-hydroxy-2'-deoxyguanosine and acrolein-lysine were significantly higher than those in the controls. Results of this study showed, even during the silent period, sustained hypercitrullinemia, hypercholesterolemia, and augmented oxidative stress in children with citrin deficiency.

Evaluation of endogenous nitric oxide synthesis in congenital urea cycle enzyme defects

Nitric oxide (NO) is synthesized from arginine and O(2) by nitric oxide synthase (NOS). Citrulline, which is formed as a by-product of the NOS reaction, can be recycled to arginine by the 2 enzymes acting in the urea cycle: argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). Although the complete urea cycle is expressed only in the liver, ASS and ASL are expressed in other organs including the kidney and vascular endothelium. To examine possible alterations of the NO pathway in urea cycle defects, we measured plasma concentrations of arginine and citrulline and serum concentrations of nitrite/nitrate (NOx(-), stable NO metabolites) and asymmetric dimethylarginine (ADMA, an endogenous NOS inhibitor) in patients with congenital urea cycle disorders of 3 types: ornithine transcarbamylase (OTC) deficiency, ASS deficiency, and ASL deficiency. All were receiving oral arginine replacement at the time of this study. The same parameters were also measured in healthy subjects, who participated as controls. The OTC-deficient patients had significantly high NOx(-) and nonsignificantly high ADMA concentrations. Their NOx(-) was significantly positively correlated with arginine. The ASS-deficient patients had significantly low NOx(-) and significantly high ADMA concentrations. The ASL-deficient patients had normal NOx(-) and nonsignificantly high ADMA concentrations. In ASS-deficient and ASL-deficient patients, the NOx(-) was significantly inversely correlated with citrulline. These results suggest that NO synthesis is enhanced in OTC-deficient patients while receiving arginine but that NO synthesis remains low in ASS-deficient patients despite receiving arginine. They also suggest that endogenous NO synthesis is negatively affected by citrulline and ADMA in ASS-deficient and ASL-deficient patients. Although the molecular mechanisms remain poorly understood, we infer that the NO pathway might play a role in the pathophysiology related to congenital urea cycle disorders.

Plasma ADMA concentrations at birth and mechanical ventilation in preterm infants: a prospective pilot study

RATIONALE

Nitric oxide (NO) produced in the lung is an important mediator of normal lung development, vascular smooth muscle relaxation, and ventilation perfusion matching. NO is synthesized from arginine by the action of NO-synthase (NOS). Asymmetric dimethylarginine (ADMA), an endogenous derivate of arginine, inhibits NOS and is thereby a determinant of NO synthesis. We compared ADMA and arginine levels in preterm infants requiring mechanical ventilation with preterm infants who did not require mechanical ventilation and determined the relation between ADMA and the length of mechanical ventilation in these infants.

METHODS

Thirty preterm infants, mean (SD) gestational age 29.3 (1.7) weeks and birth weight 1,340 (350) gram, of the Neonatal Intensive Care Unit of the VU University Medical Center were included. ADMA and arginine were measured in umbilical cord blood and the length of mechanical ventilation (days) was registered.

RESULTS

Gestational age and birth weight were significantly smaller in infants requiring mechanical ventilation, but were not significantly correlated with plasma ADMA concentration after birth. Plasma ADMA concentrations were significantly higher in infants who required mechanical ventilation than in infants who did not require mechanical ventilation (1.53 +/- 0.23 and 1.37 +/- 0.14 micromol/L, respectively; P = 0.036). ADMA concentration was significantly related to length of mechanical ventilation (B = 3.4; 95% CI: 1.1-5.6; P = 0.006), also after adjustment for gestational age (B = 2.3; 95% CI: 0.4-4.2; P = 0.024).

CONCLUSIONS

Preterm infants who require mechanical ventilation have increased ADMA levels compared to non-ventilated preterm infants. ADMA levels at birth are related to the length of mechanical ventilation. An increased ADMA concentration could reduce NO synthesis, which could lead to insufficient gas exchange and, consequently, a longer period of mechanical ventilation.