The Effect of Phosphoric Acid on the Development of Neural Tube Defects in Chick Embryos

BACKGROUND Neural tube defects (NTDs) are among the most common congenital malformations and arise from disruption of early neurulation. Phosphoric acid is a widely used food additive; however, its potential effects on early neural tube development have not previously been evaluated in experimental neurulation models. This proof-of-concept study aimed to investigate the embryotoxic and teratogenic effects of phosphoric acid on neural tube development in a chick-embryo model of neurulation, at a single tested concentration. MATERIAL AND METHODS Fertilized pathogen-free chicken eggs (n=30) were randomly allocated into 2 groups. Control embryos (n=15) received no injection, whereas embryos in the experimental group (n=15) were injected beneath the embryonic disc with 0.25 mM phosphoric acid, at Hamburger-Hamilton stage 9. Embryos were incubated for 72 hours, after which survival was recorded and neural tube development was evaluated macroscopically and histopathologically. Statistical comparisons were performed using Fisher's exact test. RESULTS All control embryos survived (15/15, 100%) and exhibited normal neural tube closure. In the phosphoric acid-treated group, survival was significantly reduced (10/15, 66.7%; P=0.0421). Among surviving treated embryos, 80% (8/10) demonstrated NTDs, including cranial and caudal closure abnormalities (P<0.001). Histopathological examination confirmed incomplete neural fold closure, irregular notochord morphology, and disrupted somite organization in affected embryos. CONCLUSIONS Phosphoric acid exposure at the tested concentration and developmental stage markedly reduced embryo survival and induced a high incidence of neural tube closure defects in a chick-embryo model. These findings provide the first experimental proof-of-concept evidence that phosphoric acid can directly disrupt early neurulation in a vertebrate neurulation model. However, vehicle-controlled replication, dose-response analyses, and exposure-bridging studies are required to distinguish teratogenic specificity from general embryotoxicity and to assess potential relevance to human embryogenesis.