Phenylalanine hydroxylase deficient phenylketonuria comparative metabolomics identifies energy pathway disruption and oxidative stress

Steven F Dobrowolski; Yu Leng Phua; Cayla Sudano; Kayla Spridik; Pascal O Zinn; Yudong Wang; Sivakama Bharathi; Jerry Vockley; Eric Goetzman

doi:10.1016/j.ymgme.2021.04.002

Phenylalanine hydroxylase deficient phenylketonuria comparative metabolomics identifies energy pathway disruption and oxidative stress

Mol Genet Metab. 2021 Apr 7:S1096-7192(21)00686-7. doi: 10.1016/j.ymgme.2021.04.002. Online ahead of print.

Authors

Steven F Dobrowolski¹, Yu Leng Phua², Cayla Sudano³, Kayla Spridik³, Pascal O Zinn⁴, Yudong Wang², Sivakama Bharathi², Jerry Vockley², Eric Goetzman²

Affiliations

¹ Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15224, United States. Electronic address: dobrowolskis@upmc.edu.
² Division of Medical Genetics, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15224, United States.
³ Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15224, United States.
⁴ Department of Neurological Surgery, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15224, United States.

PMID: 33846068
DOI: 10.1016/j.ymgme.2021.04.002

Abstract

Classical phenylketonuria (PKU, OMIM 261600) owes to hepatic deficiency of phenylalanine hydroxylase (PAH) that enzymatically converts phenylalanine (Phe) to tyrosine (Tyr). PKU neurologic phenotypes include impaired brain development, decreased myelination, early onset mental retardation, seizures, and late-onset features (neuropsychiatric, Parkinsonism). PAH deficiency leads to systemic hyperphenylalaninemia; however, the impact of Phe varies between tissues. To characterize tissue response to hyperphenylalaninemia, metabolomics was applied to tissue from therapy noncompliant classical PKU patients (blood, liver), the Pah^enu2 classical PKU mouse (blood, liver, brain) and the PAH deficient pig (blood, liver, brain, cerebrospinal fluid). In blood, liver, and CSF from both patients and animal models over-represented analytes were principally Phe, Phe catabolites, and Phe-related analytes (conjugates, Phe-containing dipeptides). In addition to Phe and Phe-related analytes, the metabolomic profile of PKU brain tissue (mouse, pig) evidenced oxidative stress responses and energy dysregulation. In Pah^enu2 and PKU pig brain tissues, anti-oxidative response by glutathione and homocarnosine is apparent. Oxidative stress in Pah^enu2 brain was further demonstrated by increased reactive oxygen species. In Pah^enu2 and PKU pig brain, an increased NADH/NAD ratio suggests a respiratory chain dysfunction. Respirometry in PKU brain mitochondria (mouse, pig) functionally confirmed reduced respiratory chain activity. Glycolysis pathway analytes are over-represented in PKU brain tissue (mouse, pig). PKU pathologies owe to liver metabolic deficiency; yet, PKU liver tissue (mouse, pig, human) shows neither energy disruption nor anti-oxidative response. Unique aspects of metabolomic homeostasis in PKU brain tissue along with increased reactive oxygen species and respiratory chain deficit provide insight to neurologic disease mechanisms. While some elements of assumed, long standing PKU neuropathology are enforced by metabolomic data (e.g. reduced tryptophan and serotonin representation), energy dysregulation and tissue oxidative stress expand mechanisms underlying neuropathology.

Keywords: Energy; Metabolomics; Oxidative stress; Phenylketonuria.