Lipid droplet-targeted ratiometric fluorescent probe for visualizing labile Fe2+ in alcohol-induced liver injury and silymarin-mediated protection.

The dysregulation of labile ferrous ions (Fe2+) is closely associated with oxidative stress, lipid peroxidation, and ferroptosis, all of which contribute to liver injury. The lipid droplet (LD) is not only a neutral lipid storage organelle but also a dynamic subcellular platform involved in lipid metabolism and stress responses. However, direct visualization of LD-associated labile Fe2+ during alcohol-induced liver injury remains challenging due to the lack of suitable LD-targeted Fe2+ imaging tools. Herein, we developed LD-Fe, a novel LD-targeted ratiometric fluorescent probe for Fe2+ imaging. Owing to its neutral and lipophilic naphthalimide-based skeleton, LD-Fe preferentially accumulates in LD, while the carbamoyl oxime moiety serves as the Fe2+-responsive recognition unit. The probe exhibits high selectivity and sensitivity toward Fe2+, favorable photophysical properties, low cytotoxicity, and good compatibility with biological imaging. Imaging results showed that LD-Fe can selectively localize in LD and enable ratiometric monitoring of Fe2+ fluctuations in living cells. Furthermore, LD-Fe can detect elevated LD-associated labile Fe2+ in liver tissues of ethanol-treated mice, while silymarin treatment attenuated this elevation. These results showed that LD-Fe can serve as a useful tool for investigating LD-associated Fe2+ changes in alcohol-induced liver injury and the corresponding therapeutic response.