Platelet Na+, K+-ATPase activity as a possible peripheral marker for the neurotoxic effects of phenylalanine in phenylketonuria

Tissue-specific activation of mitogen-activated protein kinases for expression of transthyretin by phenylalanine and its metabolite, phenylpyruvic acid

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.

Cytoskeleton of human mononuclear cells as a possible peripheral marker for phenylalanine neurotoxicity in PKU

In this work we tested human mononuclear cells as a peripheral marker to study neurotoxicity of phenylalanine (Phe). Slices of cerebral cortex of rats or human mononuclear cells were incubated with different concentrations of Phe and/or Ala in the presence of 32P-orthophosphate, the cytoskeletal fraction was extracted, and the radioactivity incorporated into intermediate filament proteins was measured. Our results show that 2 mM Phe as well as 1 mM Ala are effective in increasing the 32P in vitro incorporation into IFs in both tissues. When cerebral cortex slices or mononuclear cells were incubated with different concentrations of Phe and/or Ala, the effects on the 32P in vitro incorporation into IF proteins was compatible with an antagonistic mechanism of action of the two amino acids on the enzymes of the phosphorylating system. In addition, these blood cells may be a possible peripheral marker to study neurotoxicity of Phe in patients with PKU.