Induction of hyperphenylalaninemia in mice by ethionine and phenylalanine

Female NMRI mice were fed diets containing l-ethionine (0.1 and 0.3% w/w) and phenylalanine (3% w/w), as well as respective control diets. Ethionine, the S-ethylated analog of methionine, was shown to inhibit phenylalanine hydroxylase in vivo, whereby in vitro kinetics remained unaffected. Treatment with ethionine resulted in fatty liver, reduced ATP content of liver, and alterations in serum amino acid concentrations. In the high dosage ethionine group, for instance, concentrations of Ala, Gly, Ser, Met, and Phe were increased whereas concentrations of Lys, Asp, and Pro were decreased. Applying ethionine together with phenylalanine resulted in hyperphenylalaninemia and phenylketonuria. Feeding phenylalanine alone also led to decreased activity of phenylalanine hydroxylase and increased concentration of Phe in serum. Ethionine only had a minimal effect on body weight gain; however, the hyperphenylalaninemic condition induced by application of the high dosage of ethionine and phenylalanine induced severe loss of body weight. A disturbed protein synthesis and protein phosphorylation might be the underlying mechanism of ethionine-induced suppression of phenylalanine hydroxylase.