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Taslimifar M, Buoso S, Verrey F, Kurtcuoglu V. Propagation of Plasma L-Phenylalanine Concentration Fluctuations to the Neurovascular Unit in Phenylketonuria: An in silico Study. Front Physiol 2019; 10:360. [PMID: 31105574 PMCID: PMC6454150 DOI: 10.3389/fphys.2019.00360] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 03/14/2019] [Indexed: 01/21/2023] Open
Abstract
Phenylketonuria (PKU) is an inherited metabolic disease characterized by abnormally high concentrations of the essential amino acid L-phenylalanine (Phe) in blood plasma caused by reduced activity of phenylalanine hydroxylase (PAH). While numerous studies have shown association between high plasma Phe concentration and intellectual impairment, it is not clear whether increased Phe fluctuations also observed in PKU affect the brain as well. To investigate this, time-resolved in vivo data on Phe and competing large neutral amino acid (LNAA) concentrations in neurons are needed, but cannot be acquired readily with current methods. We have used in silico modeling as an alternative approach to characterize the interactive dynamics of Phe and competing LNAAs (CL) in the neurovascular unit (NVU). Our results suggest that plasma Phe fluctuations can propagate into the NVU cells and change there the concentration of LNAAs, with the highest magnitude of this effect observed at low frequency and high amplitude-to-mean ratio of the plasma Phe concentration fluctuations. Our model further elucidates the effect of therapeutic LNAA supplementation in PKU, showing how abnormal concentrations of Phe and CL in the NVU move thereby toward normal physiologic levels.
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Affiliation(s)
- Mehdi Taslimifar
- The Interface Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Epithelial Transport Group, Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Stefano Buoso
- The Interface Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Institute for Diagnostic and Interventional Radiology, Zurich University Hospital, Zurich, Switzerland
| | - Francois Verrey
- Epithelial Transport Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.,National Center of Competence in Research, Kidney Control of Homeostasis, Zurich, Switzerland
| | - Vartan Kurtcuoglu
- The Interface Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.,National Center of Competence in Research, Kidney Control of Homeostasis, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland
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Kumru B, Ozturk Hismi B, Kaplan DS, Celik H. Studying the effect of large neutral amino acid supplements on oxidative stress in phenylketonuric patients. J Pediatr Endocrinol Metab 2019; 32:269-274. [PMID: 30835252 DOI: 10.1515/jpem-2018-0454] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 01/16/2019] [Indexed: 11/15/2022]
Abstract
Background Oxidative stress may be one of the causes responsible for mental retardation in phenylketonuria (PKU) patients. Phenylalanine (Phe) reduces antioxidant defense and promotes oxidative stress by causing increase in reactive oxygen-nitrogen species. Our study aimed to investigate the effect of different treatments (amino acid mixture/large neutral amino acid [LNAA] supplements) on oxidative stress which are applied to late-diagnosed patients. To the best of our knowledge, this is the first study to investigate the effect of LNAA supplements on oxidative stress. Methods Twenty late-diagnosed classic PKU patients were included in this study. Patients were classified into two groups: patients under Phe-restricted diet and using Phe-free amino acid mixtures (Group I) (mean age: 13.8 ± 2.8), and patients taking LNAA supplements (Group II) (mean age: 14.8 ± 3.8). Healthy controls (mean age: 13.6 ± 4.8) with ages consistent with the ages of the patients in the experimental groups were included. Results Glutathione peroxidase is lower in patients of taking LNAA supplements than the control group (p = 0.022). Coenzyme Q10 is lower in patients of using Phe-free amino acid mixtures than the control group and it is significantly higher in Group II than Group I (p = 0.0001, p = 0.028, respectively). No significant differences were detected in total antioxidant status, total oxidant status, oxidative stress index, paraoxonase 1 and L-carnitine levels. Conclusions Different treatments affect oxidative stress parameters in PKU patients. In this study, although patients were followed up with classic PKU, patient-specific adjuvant antioxidant therapies should be implemented in response to oxidative stress.
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Affiliation(s)
- Burcu Kumru
- Division of Nutrition and Diet, Gaziantep Cengiz Gökçek Maternity and Children's Hospital, Gaziantep, Turkey, Phone: +905321623092, Fax: +03423600888
| | - Burcu Ozturk Hismi
- Division of Pediatric Metabolism and Nutrition, Tepecik Training and Research Hospital, Izmir, Turkey
| | | | - Hakim Celik
- Division of Physiology, Harran University, Sanlıurfa, Turkey
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Taslimifar M, Buoso S, Verrey F, Kurtcuoglu V. Functional Polarity of Microvascular Brain Endothelial Cells Supported by Neurovascular Unit Computational Model of Large Neutral Amino Acid Homeostasis. Front Physiol 2018; 9:171. [PMID: 29593549 PMCID: PMC5859092 DOI: 10.3389/fphys.2018.00171] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Accepted: 02/20/2018] [Indexed: 11/13/2022] Open
Abstract
The homeostatic regulation of large neutral amino acid (LNAA) concentration in the brain interstitial fluid (ISF) is essential for proper brain function. LNAA passage into the brain is primarily mediated by the complex and dynamic interactions between various solute carrier (SLC) transporters expressed in the neurovascular unit (NVU), among which SLC7A5/LAT1 is considered to be the major contributor in microvascular brain endothelial cells (MBEC). The LAT1-mediated trans-endothelial transport of LNAAs, however, could not be characterized precisely by available in vitro and in vivo standard methods so far. To circumvent these limitations, we have incorporated published in vivo data of rat brain into a robust computational model of NVU-LNAA homeostasis, allowing us to evaluate hypotheses concerning LAT1-mediated trans-endothelial transport of LNAAs across the blood brain barrier (BBB). We show that accounting for functional polarity of MBECs with either asymmetric LAT1 distribution between membranes and/or intrinsic LAT1 asymmetry with low intraendothelial binding affinity is required to reproduce the experimentally measured brain ISF response to intraperitoneal (IP) L-tyrosine and L-phenylalanine injection. On the basis of these findings, we have also investigated the effect of IP administrated L-tyrosine and L-phenylalanine on the dynamics of LNAAs in MBECs, astrocytes and neurons. Finally, the computational model was shown to explain the trans-stimulation of LNAA uptake across the BBB observed upon ISF perfusion with a competitive LAT1 inhibitor.
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Affiliation(s)
- Mehdi Taslimifar
- The Interface Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Epithelial Transport Group, Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Stefano Buoso
- The Interface Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Institute for Diagnostic and Interventional Radiology, Zurich University Hospital, Zurich, Switzerland
| | - Francois Verrey
- Epithelial Transport Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.,National Center of Competence in Research, Kidney.CH, Zurich, Switzerland
| | - Vartan Kurtcuoglu
- The Interface Group, Institute of Physiology, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.,National Center of Competence in Research, Kidney.CH, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland
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de Groot MJ, Sijens PE, Reijngoud DJ, Paans AM, van Spronsen FJ. Phenylketonuria: brain phenylalanine concentrations relate inversely to cerebral protein synthesis. J Cereb Blood Flow Metab 2015; 35:200-5. [PMID: 25352046 PMCID: PMC4426736 DOI: 10.1038/jcbfm.2014.183] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Revised: 08/19/2014] [Accepted: 09/04/2014] [Indexed: 11/09/2022]
Abstract
In phenylketonuria, elevated plasma phenylalanine concentrations may disturb blood-to-brain large neutral amino acid (LNAA) transport and cerebral protein synthesis (CPS). We investigated the associations between these processes, using data obtained by positron emission tomography with l-[1-(11)C]-tyrosine ((11)C-Tyr) as a tracer. Blood-to-brain transport of non-Phe LNAAs was modeled by the rate constant for (11)C-Tyr transport from arterial plasma to brain tissue (K1), while CPS was modeled by the rate constant for (11)C-Tyr incorporation into cerebral protein (k3). Brain phenylalanine concentrations were measured by magnetic resonance spectroscopy in three volumes of interest (VOIs): supraventricular brain tissue (VOI 1), ventricular brain tissue (VOI 2), and fluid-containing ventricular voxels (VOI 3). The associations between k3 and each predictor variable were analyzed by multiple linear regression. The rate constant k3 was inversely associated with brain phenylalanine concentrations in VOIs 2 and 3 (adjusted R(2)=0.826, F=19.936, P=0.021). Since brain phenylalanine concentrations in these VOIs highly correlated with each other, the specific associations of each predictor with k3 could not be determined. The associations between k3 and plasma phenylalanine concentration, K1, and brain phenylalanine concentrations in VOI 1 were nonsignificant. In conclusion, our study shows an inverse association between k3 and increased brain phenylalanine concentrations.
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Affiliation(s)
- Martijn J de Groot
- 1] Department of Metabolic Diseases, Beatrix Children's Hospital, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands [2] Department of Digestive and Metabolic Diseases, Center for Liver, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Paul E Sijens
- Department of Radiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Dirk-Jan Reijngoud
- 1] Department of Digestive and Metabolic Diseases, Center for Liver, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands [2] Department of Laboratory Medicine, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Anne M Paans
- Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Francjan J van Spronsen
- 1] Department of Metabolic Diseases, Beatrix Children's Hospital, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands [2] Department of Digestive and Metabolic Diseases, Center for Liver, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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Cleary M, Trefz F, Muntau AC, Feillet F, van Spronsen FJ, Burlina A, Bélanger-Quintana A, Giżewska M, Gasteyger C, Bettiol E, Blau N, MacDonald A. Fluctuations in phenylalanine concentrations in phenylketonuria: a review of possible relationships with outcomes. Mol Genet Metab 2013; 110:418-23. [PMID: 24090706 DOI: 10.1016/j.ymgme.2013.09.001] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 09/03/2013] [Indexed: 11/21/2022]
Abstract
Fluctuations in blood phenylalanine concentrations may be an important determinant of intellectual outcome in patients with early and continuously treated phenylketonuria (PKU). This review evaluates the studies on phenylalanine fluctuations, factors affecting fluctuations, and if stabilizing phenylalanine concentrations affects outcomes, particularly neurocognitive outcome. Electronic literature searches of Embase and PubMed were performed for English-language publications, and the bibliographies of identified publications were also searched. In patients with PKU, phenylalanine concentrations are highest in the morning. Factors that can affect phenylalanine fluctuations include age, diet, timing and dosing of protein substitute and energy intake, dietary adherence, phenylalanine hydroxylase genotype, changes in dietary phenylalanine intake and protein metabolism, illness, and growth rate. Even distribution of phenylalanine-free protein substitute intake throughout 24h may reduce blood phenylalanine fluctuations. Patients responsive to and treated with 6R-tetrahydrobiopterin seem to have less fluctuation in their blood phenylalanine concentrations than controls. An increase in blood phenylalanine concentration may result in increased brain and cerebrospinal fluid phenylalanine concentrations within hours. Although some evidence suggests that stabilization of blood phenylalanine concentrations may have benefits in patients with PKU, more studies are needed to distinguish the effects of blood phenylalanine fluctuations from those of poor metabolic control.
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Affiliation(s)
- Maureen Cleary
- Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK.
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Stevenson M, McNaughton N. A comparison of phenylketonuria with attention deficit hyperactivity disorder: do markedly different aetiologies deliver common phenotypes? Brain Res Bull 2013; 99:63-83. [PMID: 24140048 DOI: 10.1016/j.brainresbull.2013.10.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Revised: 09/04/2013] [Accepted: 10/07/2013] [Indexed: 01/21/2023]
Abstract
Phenylketonuria (PKU) is a well-defined metabolic disorder arising from a mutation that disrupts phenylalanine metabolism and so produces a variety of neural changes indirectly. Severe cognitive impairment can be prevented by dietary treatment; however, residual symptoms may be reported. These residual symptoms appear to overlap a more prevalent childhood disorder: Attention Deficit/Hyperactivity Disorder (ADHD). However, the aetiology of ADHD is a vast contrast to PKU: it seems to arise from a complex combination of genes; and it has a substantial environmental component. We ask whether these two disorders result from two vastly different genotypes that converge on a specific core phenotype that includes similar dysfunctions of Gray's (Gray, 1982) Behavioural Inhibition System (BIS), coupled with other disorder-specific dysfunctions. If so, we believe comparison of the commonalities will allow greater understanding of the neuropsychology of both disorders. We review in detail the aetiology, treatment, neural pathology, cognitive deficits and electrophysiological abnormalities of PKU; and compare this with selected directly matching aspects of ADHD. The biochemical and neural pathologies of PKU and ADHD are quite distinct in their causes and detail; but they result in the disorder in the brain of large amino acid levels, dopamine and white matter that are very similar and could explain the overlap of symptoms within and between the PKU and ADHD spectra. The common deficits affect visual function, motor function, attention, working memory, planning, and inhibition. For each of PKU and ADHD separately, a subset of deficits has been attributed to a primary dysfunction of behavioural inhibition. In the case of ADHD (excluding the inattentive subtype) this has been proposed to involve a specific failure of the BIS; and we suggest that this is also true of PKU. This accounts for a substantial proportion of the parallels in the superficial symptoms of both disorders and we see this as linked to prefrontal, rather than more general, dysfunction of the BIS.
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