A hemicyanine-modified upconversion nanoprobe for NIR-excited evaluating superoxide signaling in drug-induced liver injury

Background: Drug-induced liver injury (DILI) is the most important standard for the entrance of clinical drugs into the pharmaceutical market. The elevation of superoxide anion (O₂^•-) during drug metabolism can mediate apoptosis of hepatocytes and further generation of liver damage. Therefore, developing an effective imaging method for evaluating O₂^•- levels during DILI is of great importance. However, current reported O₂^•- fluorescent probes either use short excitation wavelengths or a single intensity detection system, limiting the accurate quantification of O₂^•- in deep tissue in vivo. Results: We developed a NIR-excited ratiometric nanoprobe (CyD-UCNPs) by assembly of O₂^•--sensitive hemicyanine dyes (CyD) on the surface of Tm/Er-codoped upconversion nanoparticles (UCNPs) with the assistance of α-cyclodextrin, which exhibited a robust “turn-on” ratiometric sensing signal. In vitro experiments indicated that CyD-UCNPs respond well to O₂^•- with high selectivity. Furthermore, by taking advantage of the outstanding optical properties produced by the luminescent resonance energy transfer between the UCNPs and CyD upon the excitation of 980 nm, the ratiometric upconversion luminescence signal of CyD-UCNPs was successfully utilized to monitor the fluctuation of O₂^•- levels under phorbol-12-myristate-13-acetate (PMA)/cisplatin-induced oxidative stress in living cells, liver tissues, and zebrafish. More importantly, endogenous change in O₂^•- levels in the liver sites of mice during DILI and its prevention with L-carnitine was visualized using CyD-UCNPs. Significance: This study provides a ratiometric NIR-excited imaging strategy for investigating the correlation between O₂^•- levels and DILI and its prevention, which is significant for early diagnosis of DILI and preclinical screening of anti-hepatotoxic drugs in vivo.