Fabricating a mitochondrial viscosity-activated fluorescent probe for highly sensitive imaging of kidney injury in vivo

Diabetic kidney injury has become one of the considerable causes of kidney diseases. Early detection and intervention can effectively delay the development of kidney diseases. Viscosity, as a critical parameter of the cellular microenvironment, plays a pivotal role in maintaining mitochondrial function and cellular homeostasis, and its dysregulation is closely associated with the pathogenesis of diabetic kidney injury. However, it is rarely reported that fluorescent probes are used to determine mitochondria viscosity changes in the process of diabetic kidney injury. Herein, a hemicyanine-based near-infrared (NIR) fluorescent probe P4 was developed using a “progressive optimization (PO)” strategy, enabling targeted imaging of mitochondrial viscosity changes in kidney cells and in vivo. The P4 probe possessed high sensitivity and selectivity toward viscosity and exhibited an approximately 146-fold signal enhancement in high-viscosity environments with a linear relationship (R²=0.995). And the fluorescence quantum yield (Φ) of P4 increased from < 0.001 in PBS (low viscosity) to 0.12 in 90 % glycerol (high viscosity). Moreover, P4 probe showed excellent mitochondrial localization efficiency, enabling real-time monitoring of mitochondrial viscosity changes during diabetic kidney injury progression and therapeutic intervention. In addition, P4 probe detected viscosity variations with a 1.5-fold signal intensity increase in diabetic kidney injury models compared to healthy controls in vivo. Using P4 probe, the viscosity changes related to ferroptosis were also accounted in the high glucose-induced kidney cell injury model for the first time. This work would provide a meaningful tool for gaining deeper insight into the viscosity variations in the kidney diseases, and it is expected to promote early diagnosis and treatment of kidney diseases.