Comparative Metabolomics in the Pah Classical PKU Mouse Identifies Cerebral Energy Pathway Disruption and Oxidative Stress

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). Phe over-representation is systemic; however, tissue response to hyperphenylalaninemia is not consistent. To characterize hyperphenylalaninemia tissue response, metabolomics was applied to Pah classical PKU mouse blood, liver, and brain. In blood and liver over-represented analytes were principally Phe, Phe catabolites, and Phe-related analytes (Phe-conjugates, Phe-containing dipeptides). In addition to Phe and Phe-related analytes, the metabolomic profile of Pah brain tissue evidenced oxidative stress responses and energy dysregulation. Glutathione and homocarnosine anti-oxidative responses are apparent Pah brain. Oxidative stress in Pah brain was further evidenced by increased reactive oxygen species. Pah brain presents an increased NADH/NAD ratio suggesting respiratory chain complex 1 dysfunction. Respirometry in Pah brain mitochondria functionally confirmed reduced respiratory chain activity with an attenuated response to pyruvate substrate. Glycolysis pathway analytes are over-represented in Pah brain tissue. PKU pathologies owe to liver metabolic deficiency; yet, Pah liver tissue 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.