Visualization of mitochondrial monoamine oxidase dynamics in live cells and DILI via a ratiometric NIR probe with "ICT+ESIPT" mechanism.

Monoamine oxidase (MAOs) is a key enzyme that maintains amine homeostasis and participates in liver pathological processes. Real time in situ monitoring of its activity is crucial for elucidating the mechanism of drug-induced liver injury (DILI). This study successfully constructed a ratio type fluorescent probe Cy-1 with mitochondrial targeting ability and near-infrared emission characteristics. This probe is based on MAOs catalyzed oxidative deamination reaction, and achieves fluorescence response through a clever "ICT (Intramolecular Charge Transfer) + ESIPT (Excited-State Intramolecular Proton Transfer)" dual mechanism, producing significant ratiometric signal changes in the near-infrared region. Experiments have shown that Cy-1 has a wide linear range (10-115 μg/mL), high sensitivity (0.86 μg/mL), and high selectivity in vitro, and can specifically localize to mitochondria. The probe was successfully used for in situ differential monitoring of endogenous MAOs activity in living cells, and visualized semi quantitative monitoring of MAOs activity changes in vivo was achieved in an acetaminophen (APAP) induced drug-induced liver injury (DILI) model. Cy-1 is expected to become a powerful chemical tool for understanding the mechanisms of MAOs in physiological and pathological processes, especially in the occurrence and development of diseases such as liver injury, as well as evaluating the efficacy of related drugs.