Phenylalanine and its metabolites induce embryopathies in mouse embryos in culture

The aim of this study was to determine the teratogenicity of phenylalanine (Phe) and Phe metabolites in neurulating mouse embryos. Therefore, the system of whole embryo culture was employed and D9 (neurulating) mouse embryos were exposed to Phe, phenylethylamine (PEA), phe-nylpyruvic acid (PPA), phenylacetic acid (PAA), 2-OH phenylacetic acid (2-OH PAA), and phenyllactic acid (PLA) at concentrations ranging from 0.01 mM to 10 mM for 24 hours. After 24 hours, embryos were examined for morphological abnormalities and protein content by the Lowry method. Phe at 1 and 6 mM concentrations was not teratogenic; however, 10 mM inhibited cranial neural tube closure in 82% of the embryos. PEA was the most toxic factor and concentrations of 1 and 10 mM were embryo-lethal, whereas neural tube closure defects (NTDs) were observed in 67% of the embryos at 0.1 mM. 2-OH PAA was the second most toxic metabolite with concentrations of 1 and 10 mM producing NTDs in 10 and 100% of the embryos, respectively. PLA and PAA produced no NTDs at concentrations of 1 mM, 60% at 5 mM, and 100% at 10 mM. Finally, PPA produced approximately 50% NTDs at both 1 mM and 10 mM concentrations. PLA, PAA, 2-OH PAA, and PPA produced a significant reduction in embryonic protein, and PEA and 2-OH PAA reduced yolk sac protein values. PEA, 2-OH PAA, PPA, PAA, and PLA also produced craniofacial abnormalities, i.e., incomplete expansion of the forebrain, collapse of the optic vesicle, and hypoplasia of the mandible and/or the maxilla. In summary, the results showed that the relative teratogenicity of Phe and its metabolites differs and suggested that a metabolite of Phe and/or a combination of Phe and one or more of its metabolites play a role in the phenylketonuric embryopathy.