GSE112108
Does early treatment of PKU patients with sapropterin dihydrochloride affect brain development?
Background: Phenylketonuria (PKU) is an inborn error of metabolism caused by phenylalanine hydroxylase (PAH) deficiency. Patients with mild or moderate PKU can be successfully treated with sapropterin dihydrochloride (SD) which since recently is registered for usage from the age of 4 months. SD is a pharmaceutical version of tetrahydrobiopterin (BH4), a cofactor of PAH. Similar BH4 concentrations to those observed in plasma have been found in CSF of patients after a single oral administration thus proving that SD crosses the BBB. Hyperactivity has recently been reported as a post-marketing observation in some PKU patients treated with SD. Methods: 60 or 120 ng/ml sepiapterin, a stable precursor of BH4, were applied to study the effects of BH4 on developing brain cells in 3D organotypic rat brain cell cultures at two developmental stages. Immunohistochemistry, western blotting, metabolomics and RNA sequencing were performed. Findings: BH4 and BH2 measurements confirmed a successful conversion of sepiapterin to the active form BH4. In the earlier developmental stage, brain cell specific markers showed swollen astrocytes and diminished astrocytic fibres, delayed differentiation of oligodendrocytes and perturbation of axonal elongation. Immunofluorescence for activated caspase-3 revealed an increased apoptosis rate. We also found signs of perturbated GABAergic neurotransmission. RNAseq analyses revealed a number of significantly affected genes. GO enrichment allowed to identify key biological processes. Interestingly, none of these effects was observed in the later developmental stage. We show deleterious effects of SD on developing brain cells in a rat in vitro model. This observation raises the question whether the use of SD can be recommended in very young PKU patients as currently licensed. Overall design: Examination of 3 replicates of 3D brain cell agreggates treated with 120 ng/ml sepiapterin or aggregates control (treated with PBS) at 3 different time points