The L-arginine/nitric oxide (L-Arg/NO) pathway regulates endothelial function and may play an important role in the pathogenesis of Duchenne muscular dystrophy (DMD). Yet, this pathway is poorly investigated in children suffering from DMD. Endothelial dysfunction can affect the perfusion of contracting muscles, thus leading to ischemia and hypoxia. In the present study, we tested the hypothesis that reduced NO production due to elevated synthesis of N (G),N (G)-dimethyl-L-arginine (asymmetric dimethylarginine, ADMA), an endogenous inhibitor of NO synthesis, is a possible pathophysiological mechanism for progressive intramuscular muscle ischemia and disturbed endothelial function in children with DMD. Given the possible antagonistic action of homoarginine (hArg) on ADMA, we also analyzed this amino acid. We investigated 55 male patients with DMD and 54 healthy male controls (HC; aged 11.9 ± 4.8 vs. 11.1 ± 4.9 years, mean ± SD). Urinary creatinine and metabolites of the L-Arg/NO pathway were measured in plasma and urine by GC-MS or GC-MS/MS. Urine levels of ADMA and its major urinary metabolite dimethylamine (DMA), nitrite and nitrate (P < 0.001 for all) and hArg (P = 0.002) were significantly higher in DMD patients compared to HC, while the urinary DMA/ADMA molar ratio was lower (P = 0.002). In plasma, nitrate (P < 0.001), hArg (P = 0.002) and the hArg/ADMA ratio (P < 0.001) were lower in DMD than in HC. In plasma, ADMA (631 ± 119 vs. 595 ± 129 nM, P = 0.149), arginine and nitrite did not differ between DMD and HC. In DMD, positive correlations between ADMA, DMA or nitrate excretion and the stage of disease (according to Vignos and Thompson) were found. In DMD patients on steroid medication, lower concentrations of ADMA in plasma, and of DMA, ADMA, nitrate and hArg in urine were observed compared to non-treated patients. The L-Arg/NO pathway is impaired in DMD patients, with the disease progression being clinically negatively correlated with the extent of impairment. One of the underlying mechanisms in DMD may involve insufficient antagonism of ADMA by hArg. Steroids, but not creatine supplementation, seems to improve the L-Arg/NO pathway in DMD.

To gain more understanding of the complex molecular processes underlying cleft lip/palate (CLP), we established a unique human cell bank, consisting of keratinocytes and corresponding fibroblasts from individual CLP patients as a new study tool. After their careful characterization, we used such patient-derived cell cultures as well as control keratinocytes for in vitro differentiation and proliferation assays. Foreskin-derived control cells as a group showed significant higher induction of the late differentiation markers Loricrin and Filaggrin than the group of CLP patients-derived keratinocytes. Additionally, we detected great variations between individual CLP keratinocyte cell cultures in regard to their potential to terminally differentiate as assessed by the induction of Loricrin and Filaggrin. Primary patient cell cultures that did not properly differentiate, exhibited high proliferation rates. Moreover, we could correlate the expression levels of transcription factor IRF6 to the ability of individual cell cultures to terminally differentiate. Using clinically relevant, patient-derived cells, our results suggest that some of the genetic predispositions causing CLP might also lead to deficiencies in keratinocyte differentiation manifested in in vitro assays.

Attention deficit hyperactivity disorder (ADHD) is a common pediatric psychiatric disorder, frequently treated with methylphenidate (MPH). Recently, MPH’s cardiovascular safety has been questioned by observational studies describing an increased cardiovascular risk in adults and blood pressure alterations in children. We considered members of the L-arginine (Arg)/nitric oxide (NO) pathway as possible early cardiovascular risk factors in pediatric ADHD children. They include the NO metabolites, nitrite and nitrate, the NO precursor Arg, and asymmetric dimethylarginine (ADMA), an endogenous NO synthase (NOS) inhibitor and a cardiovascular risk factor in adults. We conducted a prospective clinical trial with 42 ADHD children (aged 6–16 years) with (n = 19) and without (n = 23) MPH treatment. Age-matched children without ADHD (n = 43) served as controls. All plasma and urine metabolites were determined by gas chromatography-mass spectrometry. We observed higher plasma nitrite and lower plasma ADMA concentrations in the ADHD children. MPH-treated ADHD children had higher plasma nitrite concentrations than MPH-untreated ADHD children. As NOS activity is basally inhibited by ADMA, MPH treatment seems to have decreased the inhibitory potency of ADMA. Percentiles of systolic blood pressure were higher in MPH-treated ADHD children. The underlying mechanisms and their implications in the MPH therapy of pediatric ADHD with MPH remain to be elucidated in larger cohorts.

High circulating levels of asymmetric dimethylarginine (ADMA) and low circulating levels of homoarginine (hArg) are known cardiovascular risk factors in adults. While in adults with type 1 diabetes mellitus (T1DM) circulating ADMA is significantly elevated, in children and adolescents the reported ADMA data are contradictory. In 102 children with T1DM and 95 healthy controls (HC) serving as controls, we investigated the L-arginine (Arg)/nitric oxide (NO) pathway. Children with T1DM were divided into two groups, i.e., in children with newly diagnosed diabetes mellitus [T1DM-ND; n = 10; age, 8.8 (4.4-11.2) years; HbA1c, 13 (8.9-13.9) %] and in those with long-term treatment [T1DM-T; n = 92; age, 12.5 (10.5-15.4) years; HbA1c, 8.0 (7.2-8.6) %]. The age of the HC was 11.3 (8-13.3) years. Amino acids and NO metabolites of the Arg/NO pathway, creatinine and the oxidative stress biomarker malondialdehyde (MDA) were measured by GC-MS or GC-MS/MS. Plasma hArg, ADMA and the hArg/ADMA molar ratio did not differ between the T1DM and HC groups. There was a significant difference between T1DM-T and HC with regard to plasma nitrite [0.53 (0.48-0.61) vs 2.05 (0.86-2.36) µM, P < 0.0001] as well as to urinary nitrite [0.09 (0.06-0.17) vs 0.22 (0.13-0.37) μmol/mmol creatinine, P < 0.0001]. Plasma, but not urinary nitrite, differed between T1DM-ND and HC [0.55 (0.50-0.66) vs 2.05 (0.86-2.36) µM, P < 0.0001]. Plasma MDA did not differ between the groups. The urinary nitrate-to-nitrite molar ratio (UNOXR), a measure of nitrite-dependent renal carbonic anhydrase (CA) activity, was higher in T1DM-T [1173 (738-1481), P < 0.0001] and T1DM-ND [1341 (1117-1615), P = 0.0007] compared to HC [540 (324-962)], but did not differ between T1DM-T and T1DM-ND (P = 0.272). The lower nitrite excretion in the children with T1DM may indicate enhanced renal CA-dependent nitrite reabsorption compared with healthy children. Yet, lower plasma nitrite concentration in the T1DM patients may have also contributed to the higher UNOXR. Patients' age correlated positively with plasma hArg and hArg/ADMA and urinary DMA/ADMA. Plasma ADMA and urinary ADMA, DMA, nitrite and nitrate correlated negatively with age of the T1DM-T children. Significant correlations were found between plasma hArg and plasma Arg (r = 0.468, P < 0.0001), and urinary DMA (r = -0.426, P = 0.0001), ADMA (r = -0.266, P = 0.021) and nitrate (r = -0.234, P = 0.043). Plasma hArg correlated positively with age at diagnosis (r = +0.337, P = 0.002). ADMA, but not hArg, correlated with HbA1c in T1DM-T (r = -0.418, P < 0.0001) and T1DM-ND (r = +0.879, P = 0.0016). The greatest differences between T1DM-T and T1DM-ND were observed for urinary ADMA, DMA/ADMA ratio, nitrite and nitrate. The Arg/NO pathway is altered in T1DM in childhood and adolescence, yet the role and the importance of hArg and ADMA in T1DM remain to be elucidated. In young T1DM patients, oxidative stress (lipid peroxidation) is not elevated.

Adult subjects with growth hormone (GH) deficiency (GHD) are known to have reduced life expectancy due to increased cardiovascular and cerebrovascular events. In adults, these events are associated with elevated circulating concentrations of asymmetric dimethylarginine (ADMA) which is an endogenous inhibitor of L-arginine (Arg)-derived nitric oxide (NO). Low circulating concentrations of homoarginine (hArg) emerged as a cardiovascular risk factor. In adults, hArg seems to antagonize ADMA. In the present work, we tested the hypothesis that children with short stature without or with GHD have altered Arg/NO pathway as compared to children with normal growth. We studied 66 short stature children (38 boys, 28 girls) aged 3.5-17.3 years, who underwent the routine L-Arginine Test to diagnose presence of GHD. GHD was confirmed in 47 children (GHD group; 30 boys, 17 girls) and was absent in the remaining 19 children (non-GHD group; 8 boys, 11 girls). In addition, we investigated 24 healthy age- and gender-matched children (10 boys, 14 girls) with normal growth. In EDTA plasma samples of all children, we determined by mass spectrometry-based methods the concentrations of Arg, hArg and ADMA, and calculated the Arg/ADMA and hArg/ADMA molar ratios. With respect to these biochemical parameters, we did not find statistically significant differences between the GHD and non-GHD groups. Comparing short with normal stature children, we found small differences regarding plasma hArg concentrations [mean ± SD; median (25th-75th percentile)]: 2.06 ± 0.52 µM; 2.12 (1.74-2.36) µM vs. 1.7 ± 0.5 µM; 1.6 (1.4-1.8) µM, P < 0.001. Compared to normal stature children, short stature children had considerably higher plasma concentrations of ADMA [0.77 ± 0.15 µM; 0.77 (0.66-0.85) µM vs. 0.57 ± 0.09 µM; 0.58 (0.50-0.63) µM, P < 0.001], but not of Arg [83.3 ± 19.2 µM; 82.2 (71.9-90.3) µM vs. 86.5 ± 17.8 µM; 84.8 (77.2-94.8) µM, P = 0.336], or the hArg/ADMA ratio [2.74 ± 0.76; 2.7 (2.2-3.1) vs. 3.1 ± 1.2; 2.85 (2.42-3.66), P = 0.161. hArg in the GHD group (r = 0.41, P = 0.004) and the hArg/ADMA ratio in both groups (r = 0.44, P = 0.002 in GHD; r = 0.55, P = 0.01 in non-GHD)], but not ADMA were positively correlated with insulin-like growth factor-1 (IGF-1). hArg and hArg/ADMA differed between girls and boys in the GHD and non-GHD groups but in the normal growth group. The hArg/ADMA ratio increased with age in all groups. Our study suggests that hArg and ADMA are involved in growth in the childhood, presumably in an antagonistic manner, with ADMA slowing and hArg accelerating growth.

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