The l-arginine/NO pathway and homoarginine are altered in Duchenne muscular dystrophy and improved by glucocorticoids
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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.
KeywordsADMA Children Duchenne muscular dystrophy Homoarginine Nitric oxide Steroids
Asymmetric dimethylarginine (N G,N G-dimethyl-l-arginine)
Duchenne muscular dystrophy
Endothelium-derived relaxing factor
Gas chromatography–mass spectrometry
Gas chromatography–tandem mass spectrometry
Nitric oxide synthase
Symmetric dimethylarginine (N G,N G´-dimethyl-l-arginine)
Soluble vascular cell adhesion molecule-1
The authors thank A. Mitschke and M. T. Suchy for excellent laboratory assistance and F. M. Gutzki for performing GC–MS and GC–MS/MS analyses. We are also grateful for the support in recruiting DMD patients from the Department of Neuropediatrics in the University Hospital Essen.
Conflict of interest
The authors declare that they have no conflict of interest.
The Ethics Committees of the Faculty of Medicine at Ruhr-University Bochum and of the Hannover Medical School approved the study. Written consent was given by each participant and his parents or only by the participant if he was 18 years or older.
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