Hexavalent chromium affected eyes development in zebrafish embryos.

Hexavalent chromium (Cr (Ⅵ)) is an environmental pollutant. Previous studies have demonstrated its neurotoxic effects, however, the impact of Cr (Ⅵ) on eye development and the underlying mechanisms remain poorly understood. This study examined the effects of Cr (Ⅵ) on eye development in zebrafish embryos by assessing developmental toxicity, eye morphology, reactive oxygen species (ROS) production, apoptosis, histopathological changes, and gene expression. The results indicated that Cr (Ⅵ) exposure significantly reduced ocular axial dimensions and eye surface area. DCFH-DA and acridine orange assays showed dose-dependent increases in ROS generation and apoptosis in eyes. Histopathological analysis further confirmed nuclear pyknosis in retinal cells, as well as an increase in space between lens and retina. Additionally, the expression of antioxidant enzyme-related genes was mostly downregulated, while pro-apoptotic genes were mainly upregulated. Specific gene expression patterns in retinal cell types exhibited differential regulation: upregulation was predominantly observed in retinal ganglion cells, bipolar cells, and amacrine cells, whereas downregulation occurred in photoreceptor cells. Opsin gene expression patterns exhibited dose-dependent in a U shape type. Crystallin genes expression were mainly enhanced. Whole-mount in situ hybridization (WISH) further confirmed qRT-PCR data. This research provides the direct evidence of Cr (Ⅵ)-induced ocular toxicity.