Hyperphenylalaninemia (HPA) is an inherited metabolic disorder caused by deficiency of phenylalanine hydroxylase, characterized by significantly elevated phenylalanine levels. Conventional mechanisms, such as neurotransmitter deficiency and dysmyelination, fail to fully explain the progressive neurological damages associated with HPA. Meanwhile, ferroptosis, an emerging form of iron-dependent regulated cell death, has proven to play an important role in neurodegenerative diseases. We hereby propose a hypothesis that tetrahydrobiopterin (BH4) depletion in HPA may lead to the collapse of intracellular antioxidant defenses. This process could induce ferroptosis, thereby serving as a pivotal mechanism underlying HPA-related neurological injury. This review has systematically summarized the pathological mechanisms of HPA, the biological features of ferroptosis, and the bridging role of BH4 between them, thereby establishing a novel "HPA-BH4-ferroptosis" theoretical framework and providing a rationale for developing new therapeutic strategies targeting ferroptosis.
Ferroptosis ; Humans ; Biopterins/deficiency* ; Phenylketonurias/pathology* ; Animals

Phenylketonuria is an autosomal recessive disorder caused by a deficiency of phenylalanine hydroxylase. Transthyretin has been implicated as an indicator of nutritional status in phenylketonuria patients. In this study, we report that phenylalanine and its metabolite, phenylpyruvic acid, affect MAPK, changing transthyretin expression in a cell- and tissue-specific manner. Treatment of HepG2 cells with phenylalanine or phenylpyruvic acid decreased transcription of the TTR gene and decreased the transcriptional activity of the TTR promoter site, which was partly mediated through HNF4alpha. Decreased levels of p38 MAPK were detected in the liver of phenylketonuria-affected mice compared with wild-type mice. In contrast, treatment with phenylalanine increased transthyretin expression and induced ERK1/2 activation in PC-12 cells; ERK1/2 activation was also elevated in the brainstem of phenylketonuria-affected mice. These findings may explain between-tissue differences in gene expression, including Ttr gene expression, in the phenylketonuria mouse model.
Animals ; Brain Stem/metabolism/pathology ; Disease Models, Animal ; Gene Expression Regulation ; Hep G2 Cells ; Hepatocyte Nuclear Factor 4/metabolism ; Humans ; Liver/*metabolism/pathology ; Mice ; Mice, Mutant Strains ; Mitogen-Activated Protein Kinase 3/genetics/*metabolism ; Organ Specificity ; Phenylalanine/metabolism ; Phenylalanine Hydroxylase/deficiency ; Phenylketonurias/*genetics/metabolism/pathology/physiopathology ; Phenylpyruvic Acids/metabolism ; Prealbumin/*biosynthesis/genetics ; p38 Mitogen-Activated Protein Kinases/genetics/*metabolism

OBJECTIVETo observe brain white matter changes in children with late-treated phenylketonuria (PKU) before and after receiving treatment.

METHODSThis study included 19 PKU patients (aged 34-410 weeks) who were administered a low-phenylalanine diet (< 15-50 mg/kg daily) for 8-16 months. The brain MR imaging with spin-echo T1-weighted and T2-weighted sequences in coronal and axial planes was taken before and after treatment. The white matter abnormalities (T2WI high signal intensity) were graded based on the Thompson grading system. Meanwhile the intelligence quotient (IQ) or developmental quotient (DQ) was tested by the Gesell's Intelligence Scale.

RESULTSAll 19 PKU patients presented with the brain white matter lesions, manifesting abnormally high T2-signal intensity in the periventricular region around anterior and posterior horns of both lateral ventricles. Different extents of mental retardation were also observed in the 19 patients. The low phenylalanine diet treatment decreased the average grade of abnormal T2-signal intensity from 2.59 to 1.76 (P < 0.05). The mean IQ or DQ improved from 44.8 to 61.6 after treatment (P < 0.05). There was some correlation between the amelioration of brain white matter lesions and IQ or DQ.

CONCLUSIONSThe patients with late-treated PKU have a higher occurrence of the brain white matter lesions and mental retardation. A low-phenylalanine diet treatment can partly improve the abnormalities. Brain white matter lesions may play a part in mental retardation.

Brain ; pathology ; Child ; Child, Preschool ; Female ; Humans ; Infant ; Intelligence ; Magnetic Resonance Imaging ; Male ; Phenylalanine ; blood ; Phenylketonurias ; blood ; pathology ; psychology ; therapy

To have more insight into the mechanism of neuronal injury in phenylketonuria patients, gene expression profiles were studied in cell culture of embryonic rat cortical neurons induced by phenylalanine. Randomly chosen cortical cultures for 3 d were treated by 0.9 mmol/L phenylalanine for 12 h. Control group of the same batch was treated with the same volume of medium. Total RNA was extracted and hybridized with the Affymetrix gene chip U34 according to the protocol provided by the Affymetrix Company. Real-time PCR was used to further confirm the result. We found that the hybridization signals of 167 genes were increased among the total 1323 probes plotted on the chip. The 167 increased genes could be functionally categorized into signal transduction, neuron related, cytoskeleton, metabolism, ion channels, transcription factors, cytokines, and apoptosis related. Signals of 7 probes were decreased, which accounted to 0.5% of the total number. A series of genes that were not reported before were up-regulated by phenylalanine, including Ca(2+)/calmodulin-dependent protein kinase, Brain type II (CaMK II), Ras, P38 MAP kinase, L-voltage dependent calcium channel, some genes related to vesicle formation and transmitter release, some glutamate receptor subunits and glutamate transporters. According to the gene expression profile, it is likely that multi-processes are involved in the neuronal injury induced by high phenylalanine, such as the activation of the NMDR-Ca(2+)- CaMK II - Ras- P38 axis, the abnormality in neurotransmitter release. Our study also suggests that the excitatory neurotransmitter glutamate may play a role in the neural pathology of phenylketonuria.
Animals ; Calcium-Calmodulin-Dependent Protein Kinase Type 2 ; Calcium-Calmodulin-Dependent Protein Kinases ; genetics ; Cells, Cultured ; Cerebral Cortex ; metabolism ; pathology ; Embryo, Mammalian ; Gene Expression Profiling ; Neurons ; metabolism ; pathology ; Oligonucleotide Array Sequence Analysis ; Phenylalanine ; toxicity ; Phenylketonurias ; genetics ; pathology ; Random Allocation ; Rats ; Rats, Sprague-Dawley