Mancozeb induces cytotoxicity and functional impairment in bovine mammary epithelial cells through ER stress, oxidative stress, and inflammatory responses

Mancozeb (MZ), a broad-spectrum ethylene-bisdithiocarbamate (EBDC) fungicide used extensively for crop. MZ is characterized by its nonspecific mode of action and broad applicability; however, its low biodegradability and environmental persistence have raised biological safety concerns, particularly regarding feeding crops consumed by livestock. We investigated the effects of MZ exposure on the viability and function of bovine mammary epithelial cells (MAC-T), which play essential roles in milk synthesis and secretion, and serve as the first line of immune defense within the mammary gland. MAC-T cells were treated with 0, 1, 5, and 10 µM MZ, resulting in a significant, dose-dependent reduction in cell viability. Quantitative real-time polymerase chain reaction analysis revealed a significant upregulation of endoplasmic reticulum (ER) stress-related genes–including CHOP , BiP/GRP78 , ATF4 , and IRE1ɑ– and inflammatory markers, such as COX2 and CEBPD . At the protein level, MZ exposure significantly upregulated apoptosis-associated proteins including cleaved caspase-3 (CC3) and BAD, whereas it markedly downregulated mRNA expression of milk synthesis-related genes, β-casein ( CSN2 ), and α-lactalbumin ( LALBA ). MZ concentration-dependently reduced the density and barrier function of MAC-T epithelial monolayers, as measured by transepithelial electrical resistance. Collectively, these findings demonstrate that MZ induces ER stress, inflammatory, and pro-apoptotic responses in MAC-T cells, causing impaired cellular viability and functional integrity. Although MZ general toxicity has been previously documented, its direct effects on MAC-T cells remain largely unknown. Here, we delineated the molecular mechanisms underlying MZ-induced cytotoxicity in MAC-T cells and emphasized their potential impact on milk production safety in the dairy industry.