Non-invasive detection of hepatic cathepsin B upregulation following ischemia-reperfusion using an activatable probe

Hepatic ischemia-reperfusion (I-R) injury is a critical clinical condition lacking methods for real-time visualization of its key enzymatic activity. To address this, we developed WK-catB , an activatable optical probe targeting cathepsin B (catB), based on a sulfur-substituted hemicyanine scaffold. This probe exhibits minimal background fluorescence and photoacoustic signal in its native state but undergoes significant enhancement upon catB-mediated cleavage, enabling sensitive and selective detection of enzyme activity. In vitro assays demonstrated high specificity, low detection limit, and excellent biocompatibility. Using a murine I-R model, we successfully visualized upregulated catB activity in injured livers via both fluorescence and photoacoustic imaging, which was corroborated by ex vivo immunofluorescence, histopathology, and serum analysis. These findings highlight WK-catB as a promising tool for non-invasive monitoring of catB-related pathologies.