Effect of Zinc Oxide Nanoparticles From Infant Formula Milk Powder on Colon Cells In Vitro

Zinc is an essential trace element that participates in numerous metabolic processes; however, excessive exposure may interfere with the absorption of other metals, such as copper. In recent years, nanotechnology has experienced rapid growth, and zinc oxide nanoparticles (ZnO NPs) have garnered significant attention due to their versatile physicochemical properties and increasing applications in industrial and consumer products. These nanoparticles are widely incorporated into plastics, ceramics, cosmetics, and even infant formula milk powder for their antimicrobial and nutritional properties. Given concerns about the presence of ZnO NPs in commercial infant formula milk powder, this work examines cytotoxicity, reactive oxygen species (ROS) generation, and effects on the cell cycle. The results show that ZnO NPs isolated from commercial infant formula milk powder induced concentration-dependent cytotoxicity, triggered intracellular ROS overproduction, and cell-cycle arrest (primarily in S and G2/M phases), suggesting that oxidative stress could be a key mechanism involved in ZnO NPs-induced toxicity. Although bulk ZnO is generally recognized as safe and despite approval by the U.S. FDA for certain applications, several studies have shown that ZnO NPs can induce cytotoxic effects depending on their size, shape, and concentration. The mechanisms underlying the toxicity of ZnO NPs remain unclear. Therefore, in this work, their biological effects on intestinal epithelial cell models, such as Caco-2 and HT29 cells, were studied to assess the potential toxicity of ZnO nanoparticles present in infant milk formula. This is important for a better understanding of the potential health implications of ingesting zinc oxide nanoparticles through fortified food products.