title: Large Neutral Amino Acid Supplementation Exerts Its Effect through Three Synergistic Mechanisms: Proof of Principle in Phenylketonuria Mice.
abstract: BACKGROUND
  Phenylketonuria (PKU) was the first disorder in which severe neurocognitive dysfunction could be prevented by dietary treatment. However, despite this effect, neuropsychological outcome in PKU still remains suboptimal and the phenylalanine-restricted diet is very demanding. To improve neuropsychological outcome and relieve the dietary restrictions for PKU patients, supplementation of large neutral amino acids (LNAA) is suggested as alternative treatment strategy that might correct all brain biochemical disturbances caused by high blood phenylalanine, and thereby improve neurocognitive functioning.
  
  
  OBJECTIVE
  As a proof-of-principle, this study aimed to investigate all hypothesized biochemical treatment objectives of LNAA supplementation (normalizing brain phenylalanine, non-phenylalanine LNAA, and monoaminergic neurotransmitter concentrations) in PKU mice.
  
  
  METHODS
  C57Bl/6 Pah-enu2 (PKU) mice and wild-type mice received a LNAA supplemented diet, an isonitrogenic/isocaloric high-protein control diet, or normal chow. After six weeks of dietary treatment, blood and brain amino acid and monoaminergic neurotransmitter concentrations were assessed.
  
  
  RESULTS
  In PKU mice, the investigated LNAA supplementation regimen significantly reduced blood and brain phenylalanine concentrations by 33% and 26%, respectively, compared to normal chow (p<0.01), while alleviating brain deficiencies of some but not all supplemented LNAA. Moreover, LNAA supplementation in PKU mice significantly increased brain serotonin and norepinephrine concentrations from 35% to 71% and from 57% to 86% of wild-type concentrations (p<0.01), respectively, but not brain dopamine concentrations (p = 0.307).
  
  
  CONCLUSIONS
  This study shows that LNAA supplementation without dietary phenylalanine restriction in PKU mice improves brain biochemistry through all three hypothesized biochemical mechanisms. Thereby, these data provide proof-of-concept for LNAA supplementation as a valuable alternative dietary treatment strategy in PKU. Based on these results, LNAA treatment should be further optimized for clinical application with regard to the composition and dose of the LNAA supplement, taking into account all three working mechanisms of LNAA treatment.
authors.affiliation: University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Groningen, The Netherlands.|University of Groningen, Center of Behavior and Neurosciences, Department of Molecular Neurobiology, Groningen, The Netherlands.
authors.forename: Danique
authors.initials: D
authors.lastname: van Vliet
authors.affiliation: University of Groningen, Center of Behavior and Neurosciences, Department of Molecular Neurobiology, Groningen, The Netherlands.
authors.forename: Vibeke M
authors.initials: VM
authors.lastname: Bruinenberg
authors.affiliation: University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Groningen, The Netherlands.|University of Groningen, Center of Behavior and Neurosciences, Department of Molecular Neurobiology, Groningen, The Netherlands.
authors.forename: Priscila N
authors.initials: PN
authors.lastname: Mazzola
authors.affiliation: University of Groningen, University Medical Center Groningen, Department of Laboratory Medicine, Groningen, The Netherlands.
authors.forename: Martijn H J R
authors.initials: MH
authors.lastname: van Faassen
authors.affiliation: University of Groningen, University Medical Center Groningen, Department of Laboratory Medicine, Groningen, The Netherlands.
authors.forename: Pim
authors.initials: P
authors.lastname: de Blaauw
authors.affiliation: University of Groningen, University Medical Center Groningen, Department of Laboratory Medicine, Groningen, The Netherlands.
authors.forename: Ido P
authors.initials: IP
authors.lastname: Kema
authors.affiliation: University of Groningen, University Medical Center Groningen, Department of Laboratory Medicine, Groningen, The Netherlands.
authors.forename: M Rebecca
authors.initials: MR
authors.lastname: Heiner-Fokkema
authors.affiliation: Independent Researcher, Deventer, The Netherlands.
authors.forename: Rogier D
authors.initials: RD
authors.lastname: van Anholt
authors.affiliation: University of Groningen, Center of Behavior and Neurosciences, Department of Molecular Neurobiology, Groningen, The Netherlands.
authors.forename: Eddy A
authors.initials: EA
authors.lastname: van der Zee
authors.affiliation: University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Groningen, The Netherlands.
authors.forename: Francjan J
authors.initials: FJ
authors.lastname: van Spronsen
mesh_terms: D021542:Amino Acids, Neutral / Q000627:therapeutic use*; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D019587:Dietary Supplements; D004195:Disease Models, Animal; D004298:Dopamine / Q000032:analysis; D005260:Female; D008297:Male; D051379:Mice; D019965:Neurocognitive Disorders / Q000517:prevention & control; D010649:Phenylalanine / Q000032:analysis; D010661:Phenylketonurias / Q000178:diet therapy*; D012701:Serotonin / Q000032:analysis
chemical_list: D021542:Amino Acids, Neutral; D012701:Serotonin; D010649:Phenylalanine; D004298:Dopamine