Enhanced Nitric Oxide (NO) and Decreased ADMA Synthesis in Pediatric ADHD and Selective Potentiation of NO Synthesis by Methylphenidate

Metabolomic Markers in Attention-Deficit/Hyperactivity Disorder (ADHD) among Children and Adolescents-A Systematic Review

Attention-Deficit/Hyperactivity Disorder (ADHD), characterized by clinical diversity, poses diagnostic challenges often reliant on subjective assessments. Metabolomics presents an objective approach, seeking biomarkers for precise diagnosis and targeted interventions. This review synthesizes existing metabolomic insights into ADHD, aiming to reveal biological mechanisms and diagnostic potentials. A thorough PubMed and Web of Knowledge search identified studies exploring blood/urine metabolites in ADHD-diagnosed or psychometrically assessed children and adolescents. Synthesis revealed intricate links between ADHD and altered amino acid metabolism, neurotransmitter dysregulation (especially dopamine and serotonin), oxidative stress, and the kynurenine pathway impacting neurotransmitter homeostasis. Sleep disturbance markers, notably in melatonin metabolism, and stress-induced kynurenine pathway activation emerged. Distinct metabolic signatures, notably in the kynurenine pathway, show promise as potential diagnostic markers. Despite limitations like participant heterogeneity, this review underscores the significance of integrated therapeutic approaches targeting amino acid metabolism, neurotransmitters, and stress pathways. While guiding future research, this overview of the metabolomic findings in ADHD suggests directions for precision diagnostics and personalized ADHD interventions.

Paper-based electrochemical immunosensor for the determination of symmetric dimethylarginine

In this work, we present the development of an immunosensor for the direct, selective, and sensitive determination of symmetric dimethylarginine (SDMA) in urine, in view of the emerging role of this molecule as a biomarker for renal disease. SDMA is almost completely excreted by the kidneys, hence in renal dysfunction, the excretion is decreased, resulting in accumulation in plasma. Reference values for plasma or serum have already been established in small animal practice. Values < 15 μg/dL are considered normal, 15-19 μg/dL are values of concern, and at values > 20 μg/dL kidney disease is likely. The proposed electrochemical paper-based sensing platform uses anti-SDMA antibodies for targeted detection of SDMA. Quantification is related to a decrease in the signal of a redox indicator due to the formation of an immunocomplex that interferes with electron transfer. Square wave voltammetry measurements showed a linear correlation of the peak decline for 50 nM - 1 μM SDMA with a detection limit of 15 nM. The influence of common physiological interferences caused no significant peak reduction, indicating excellent selectivity. The proposed immunosensor was successfully applied for the quantification of SDMA in human urine of healthy individuals. Surveillance of SDMA concentration in urine could prove to be very valuable in the diagnosis or monitoring of renal disease.

l-Arginine/nitric oxide pathway and oxidative stress in adults with ADHD: Effects of methylphenidate treatment

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is a mental disorder that was once thought to occur only in children. Meanwhile, it is known that adults can also be affected. The first-line drug in children and adults to treat symptoms of inattention, impulsivity, lack of self-regulation, and hyperactivity is methylphenidate (MPH). Known adverse effects of MPH include cardiovascular problems, such as elevated blood pressure and heart rate. Therefore, biomarkers to monitor potential cardiovascular side effects of MPH are needed. The l-Arginine/Nitric oxide (Arg/NO) pathway is involved in noradrenaline and dopamine release as well as in normal cardiovascular functioning and is therefore a prime candidate for the search of biomarkers. The aim of the present study was to investigate the Arg/NO pathway as well as oxidative stress in adult ADHD patients in plasma and urine and the potential influence of MPH medication.

METHODS

In plasma and urine samples of 29 adults with ADHD (39.2 ± 10.9 years) and 32 healthy adults serving as controls (CO) (38.0 ± 11.6 years) the major NO metabolites nitrite and nitrate, Arg, the NO synthesis inhibitor asymmetric dimethylarginine (ADMA) and its major urinary metabolite dimethylamine (DMA) as well as malondialdehyde (MDA) were measured by gas chromatography-mass spectrometry.

RESULTS

Of the 29 patients with ADHD 14 were currently without MPH treatment (-MPH) and 15 were treated with MPH (+MPH). Plasma nitrate concentrations were significantly higher in patients not treated with MPH vs. CO (-MPH 60.3 μM [46.2-76.0] vs. CO 44.4 μM [35.0-52.7]; p = 0.002), while plasma nitrite tended to be higher in -MPH patients (2.77 μM [2.26-3.27]) vs. CO (2.13 μM [1.50-2.93]; p = 0.053). Additionally, plasma creatinine concentrations were significantly different, with -MPH showing significantly higher concentrations than the other two groups (-MPH 141 μM [128-159]; +MPH 96.2 μM [70.2-140]; Co 75.9 μM [62.0-94.7]; p < 0.001). Urinary creatinine excretion tended to be lowest in -MPH group vs. +MPH and CO (-MPH 11.4 ± 8.88 mM; +MPH 20.7 ± 9.82 mM; 16.6 ± 7.82 mM; p = 0.076). None of the other metabolites, including MDA, a marker of oxidative stress, showed a difference between the groups.

CONCLUSION

Adult patients with ADHD, who are not treated with MPH (-MPH), showed varied Arg/NO pathway, but Arg bioavailability seemed to be consistent over the groups. Our findings imply that urinary reabsorption may be increase and/or excretion of nitrite and nitrate may be decreased in ADHD, resulting in an increase in the plasma concentration of nitrite. MPH seems to partially reverse these effects by not yet known mechanisms, and does not affect oxidative stress.

Altered Arginine/Nitric Oxide Pathway in Children Diagnosed Attention Deficit Hyperactivity Disorder, and the Effect of 10 Weeks Methylphenidate Treatment

Objective

In this study, we investigated the levels of arginine, nitric oxide (NO), asymmetric dimethylarginine (ADMA), and adrenomedullin that are presumed to play a role in attention deficit hyperactivity disorder (ADHD) etiology, and to compare the findings with healthy controls.

Methods

Thirty ADHD patients and thirty healthy control subjects aged 6−12 years were included in the study. Sociodemographic data form, Schedule for Affective Disorders and Schizophrenia for School Age Children-Present and Lifetime Version; Conners’ Parent/Teacher Rating Scale-Revised Long Form; Children’s Depression Inventory; and The State-Trait Anxiety Inventory for Children were applied to all cases. All participants included in the study were evaluated in terms of their serum arginine, NO, ADMA, and adrenomedullin levels. Subsequently, methylphenidate treatment was started in ADHD patients and blood parameters were tested again in the tenth week of treatment.

Results

At the start of the study, arginine and ADMA levels were significantly higher and NO and adrenomedullin levels were significantly lower in the ADHD group compared to the control group. Post-treatment arginine and ADMA levels were found to be significantly lower than in the pre-treatment period. There were no significant differences in NO and adrenomedullin levels before and after treatment. There was no correlation between scale scores and blood parameters.

Conclusion

These variations in the blood parameters of the ADHD group seem to be worth further investigation. Studies to be conducted with larger sample groups after longer-term treatment may provide new information about the alterations in neurobiological processes related to ADHD etiology and treatment.

Characterization of the L-Arginine/Nitric Oxide Pathway and Oxidative Stress in Pediatric Patients with Atopic Diseases

Introduction: L-Arginine (Arg) is a semi-essential amino acid. Constitutive and inducible nitric oxide synthase (NOS) isoforms convert Arg to nitric oxide (NO), a potent vaso- and bronchodilator with multiple biological functions. Atopic dermatitis (AD) and bronchial asthma (BA) are atopic diseases affecting many children globally. Several studies analyzed NO in airways, yet the systemic synthesis of NO in AD and BA in children with BA, AD or both is elusive. Methods: In a multicenter study, blood and urine were obtained from 130 of 302 participating children for the measurement of metabolites of the Arg/NO pathway (BA 31.5%; AD 5.4%; AD + BA 36.1%; attention deficit hyperactivity disorder (ADHD) 12.3%). In plasma and urine amino acids Arg and homoarginine (hArg), both substrates of NOS, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), both inhibitors of NOS, dimethylamine (DMA), and nitrite and nitrate, were measured by gas chromatography–mass spectrometry. Malondialdehyde (MDA) was measured in plasma and urine samples to evaluate possible effects of oxidative stress. Results: There were no differences in the Arg/NO pathway between the groups of children with different atopic diseases. In comparison to children with ADHD, children with AD, BA or AD and BA had higher plasma nitrite (p < 0.001) and nitrate (p < 0.001) concentrations, suggesting higher systemic NO synthesis in AD and BA. Urinary excretion of DMA was also higher (p = 0.028) in AD and BA compared to patients with ADHD, suggesting elevated ADMA metabolization. Discussion/Conclusion: The Arg/NO pathway is activated in atopic diseases independent of severity. Systemic NO synthesis is increased in children with an atopic disease. Plasma and urinary MDA levels did not differ between the groups, suggesting no effect of oxidative stress on the Arg/NO pathway in atopic diseases.

Activated L-Arginine/Nitric Oxide Pathway in Pediatric Cystic Fibrosis and Its Association with Pancreatic Insufficiency, Liver Involvement and Nourishment: An Overview and New Results

Cystic fibrosis (CF; OMIM 219700) is a rare genetic disorder caused by a chloride channel defect, resulting in lung disease, pancreas insufficiency and liver impairment. Altered L-arginine (Arg)/nitric oxide (NO) metabolism has been observed in CF patients’ lungs and in connection with malnutrition. The aim of the present study was to investigate markers of the Arg/NO pathway in the plasma and urine of CF patients and to identify possible risk factors, especially associated with malnutrition. We measured the major NO metabolites nitrite and nitrate, Arg, a semi-essential amino acid and NO precursor, the NO synthesis inhibitor asymmetric dimethylarginine (ADMA) and its major urinary metabolite dimethylamine (DMA) in plasma and urine samples of 70 pediatric CF patients and 78 age-matched healthy controls. Biomarkers were determined by gas chromatography–mass spectrometry and high-performance liquid chromatography. We observed higher plasma Arg (90.3 vs. 75.6 µM, p < 0.0001), ADMA (0.62 vs. 0.57 µM, p = 0.03), Arg/ADMA ratio (148 vs. 135, p = 0.01), nitrite (2.07 vs. 1.95 µM, p = 0.03) and nitrate (43.3 vs. 33.1 µM, p < 0.001) concentrations, as well as higher urinary DMA (57.9 vs. 40.7 µM/mM creatinine, p < 0.001) and nitrate (159 vs. 115 µM/mM creatinine, p = 0.001) excretion rates in the CF patients compared to healthy controls. CF patients with pancreatic sufficiency showed plasma concentrations of the biomarkers comparable to those of healthy controls. Malnourished CF patients had lower Arg/ADMA ratios (p = 0.02), indicating a higher NO synthesis capacity in sufficiently nourished CF patients. We conclude that NO production, protein-arginine dimethylation, and ADMA metabolism is increased in pediatric CF patients. Pancreas and liver function influence Arg/NO metabolism. Good nutritional status is associated with higher NO synthesis capacity and lower protein-arginine dimethylation.

Urinary Dimethylamine (DMA) and Its Precursor Asymmetric Dimethylarginine (ADMA) in Clinical Medicine, in the Context of Nitric Oxide (NO) and Beyond

Asymmetric protein-arginine dimethylation is a major post-translational modification (PTM) catalyzed by protein-arginine methyltransferase (PRMT). Regular proteolysis releases asymmetric dimethylarginine (ADMA). Of the daily produced ADMA, about 10% are excreted unchanged in the urine. The remaining 90% are hydrolyzed by dimethylarginine dimethylaminohydrolase (DDAH) to L-citrulline and dimethylamine (DMA), which is readily excreted in the urine. The PRMT/DDAH pathway is almost the exclusive origin of urinary ADMA and the major source of urinary DMA. Dietary fish and seafood represent additional abundant sources of urinary DMA. The present article provides an overview of urinary ADMA and DMA reported thus far in epidemiological, clinical and pharmacological studies, in connection with the L-arginine/nitric oxide (NO) pathway and beyond, in neonates, children and adolescents, young and elderly subjects, males and females. Discussed diseases mainly include those relating to the renal and cardiovascular systems such as peripheral arterial occlusive disease, coronary artery disease, chronic kidney disease, rheumatoid arthritis, Becker muscular disease, Duchenne muscular disease (DMD), attention deficit hyperactivity disorder (ADHD), and type I diabetes. Under standardized conditions involving the abstinence of DMA-rich fresh and canned fish and seafood, urinary DMA and ADMA are useful as measures of whole-body asymmetric arginine-dimethylation in health and disease. The creatinine-corrected excretion rates of DMA range from 10 to 80 µmol/mmol in adults and up to 400 µmol/mmol in children and adolescents. The creatinine-corrected excretion rates of ADMA are on average 10 times lower. In general, diseases are associated with higher urinary DMA and ADMA excretion rates, and pharmacological treatment, such as with steroids and creatine (in DMD), decreases their excretion rates, which may be accompanied by a decreased urinary excretion of nitrate, the major metabolite of NO. In healthy subjects and in rheumatoid arthritis patients, the urinary excretion rate of DMA correlates positively with the excretion rate of dihydroxyphenylglycol (DHPG), the major urinary catecholamines metabolite, suggesting a potential interplay in the PRMT/DDAH/NO pathway.