A polarity-responsive lipid droplet-targeted fluorescent probe for foam cell imaging and anti-atherosclerotic natural bioactive compounds screening

Intracranial atherosclerosis often causes severe neurosurgical cerebrovascular diseases through foam cell lipid deposition and oxidative stress. Visualizing lipid droplets and oxidative stress in foam cells aids lesion study and screening of vasoprotective natural products. We designed a polarity-responsive fluorescent probe, AFA, with solvent-dependent solvatochromism for foam cell imaging and anti-atherosclerotic screening. Probe AFA emits strong fluorescence at 592 nm in lipophilic environments, serving as the main imaging signal. In water/1,4-dioxane mixtures, probe AFA's fluorescence varies with solvent polarity. The probe remained optically stable for at least 80 min, effective across 6.0-11.0, and resisted biological interference. Experiments with edible oils confirmed its ability to distinguish hydrophobic lipid microenvironments from aqueous media. Biological tests show low cytotoxicity and good biocompatibility in RAW264.7 cells. Confocal microscopy reveals that probe AFA selectively localizes to lipid droplets in oxidized low-density lipoprotein (Ox-LDL)-induced foam cells, with fluorescence intensity correlating with Ox-LDL levels. Antioxidant treatments confirm that fluorescence intensity correlates with lipid droplet accumulation from intracellular oxidative stress, indirectly reflecting cellular redox state. We further use probe AFA to assess six bioactive compounds from Salvia miltiorrhiza for their ability to reduce oxidative stress in foam cells, demonstrating its utility for screening anti-atherosclerotic agents. Probe AFA's polarity-gated "off-on" emission at 592 nm upon lipid droplet targeting and capability to indirectly assess cellular oxidative stress by monitoring lipid droplet accumulation make it a versatile tool for lipid droplet imaging, redox-state monitoring, and identifying cerebroprotective natural compounds targeting intracranial atherosclerosis in neurosurgical research.