Fenoxycarb disrupts calcium homeostasis and impairs unfolded protein response and autophagy, leading to cell death in bovine mammary epithelial cells

Fenoxycarb is a carbamate pesticide that negatively affects the environment and harms various non-target organisms. Despite its common use in controlling fleas and mosquitoes that are often found in cattle feedlots, the toxic effects of fenoxycarb on cattle have not yet been studied. Considering the pivotal role of cattle in milk production, this study examined the effect of fenoxycarb on bovine mammary epithelial cells (MAC-T) to assess its potential risks for the lactation system. Fenoxycarb reduced cell viability and growth in both 2D and 3D cultures and increased apoptosis. Furthermore, it triggered sub-G1 phase arrest of the cell cycle, accompanied by a pronounced decrease in CCND1 and PCNA expression. Disruption of calcium homeostasis was demonstrated by a marked decline in calcium levels in both the cytosol and the mitochondria. This reduction ultimately led to the collapse of the overall calcium balance, which in turn is closely associated with a decrease in mitochondrial respiration. In addition, fenoxycarb triggered endoplasmic reticulum stress while suppressing the unfolded protein response, especially by inhibiting the EIF2A-GADD153 signaling pathway. Moreover, decreased expression of autophagy-related proteins and diminished formation of acidic vesicular organelles confirmed the occurrence of autophagy. This study highlights the potential adverse effects of fenoxycarb on the dairy industry by elucidating its toxicity mechanisms in bovine mammary glands.