Diagnosing sepsis-induced acute lung hypoxia with a mitochondria- targeted far-red nitroreductase-responsive fluorescent probe

Sepsis-induced acute lung injury (ALI) is a primary reason of death in patients with sepsis. Increasing evidence shows that mitochondrial hypoxia may cause mitochondrial dysfunction which is one of the critical mechanisms participating in sepsis-induced ALI pathogenesis. Thus, constructing the fluorescent probes to test the level of mitochondrial hypoxia during the course of sepsis-induced ALI is necessary for obtaining more knowledge about the critical role of mitochondria hypoxia in sepsis-induced ALI. Herein, fluorescent probes FL-NTR1 and FL-NTR2 were constructed by choosing the flavylium dye as the fluorescence reporting unit and mitochondrial localization group for precisely monitoring and assessing the hypoxia level via the indirect sensing of nitroreductase (NTR). FL-NTR1 and FL-NTR2 were mainly nonfluorescent. Upon selectively reacted with NTR, the parent dye FL or FL-NO2 was afforded, thereby causing a remarkable fluorescence enhancement (Absmax/Emmax = 570/640, 650 nm). Due to the superior fluorescence response to NTR and low cytotoxicity, FL-NTR1 and FL-NTR2 were utilized to test the variation of NTR level in living cells and zebrafish under various stimulants. Compared with FL-NTR1, FL-NTR2 exhibited a better mitochondria-targetable capacity, and thus, the upregulation of mitochondrial NTR level in the sepsis-induced ALI and downregulation of mitochondrial NTR level in the prolyl hydroxylase inhibitor therapy group were visualized and accurately evaluated for the first time through the utilization of FL-NTR2. This research provides a powerful new tool for accurately detecting and evaluating the tailored treatment outcome of sepsis-induced ALI.