NAG-activatable near-infrared fluorescent probe for imaging-guided diagnosis and therapeutic evaluation of kidney diseases

Early diagnosis of kidney diseases remains challenging because conventional renal function indicators are often insensitive to early renal injury. N-acetyl-β- D -glucosaminidase (NAG), a lysosomal hydrolase released from damaged proximal renal tubular epithelial cells, is a sensitive urinary biomarker of renal tubular injury. However, existing NAG-responsive fluorescent probes are limited by their short emission wavelengths and insufficient capacity for in vivo imaging. In this work, we developed an NAG-activatable near-infrared fluorescent probe, FH-NAG, by introducing an N-acetyl-β- D -glucosamine recognition unit into the near-infrared fluorophore FH-OH. FH-NAG was specifically activated by NAG, leading to the release of FH-OH, thereby producing a strong fluorescence signal at 670 nm with a large Stokes shift of 150 nm. The probe exhibited high sensitivity, excellent selectivity, good stability, and low cytotoxicity. FH-NAG was successfully employed to image endogenous NAG in living cells and distinguish between renal cancer cells and normal renal tubular epithelial cells. In vivo imaging further demonstrated the probe’s ability to visualize renal tumors and monitor NAG upregulation in acute kidney injury and STZ-induced early diabetic renal injury model. Importantly, FH-NAG was able to detect urinary NAG activity and evaluate the therapeutic response of glutathione or metformin treatment. Clinical sample analysis confirmed the probe’s ability to distinguish patients with kidney diseases from healthy controls. These findings show that FH-NAG is a promising near-infrared imaging probe for NAG activity-based diagnosis and monitoring of kidney diseases.