In situ mapping of HSA reabsorption by a NIR fluorogenic sensor as a practical phenotypic assay for nephroprotective drug discovery.

The impaired reabsorption of kidney tubules is a critical early event in drug-induced kidney injury (DIKI), making real-time monitoring of human serum albumin (HSA) endocytosis essential for assessing renal function and screening nephroprotective agents. Inspired by the specific warfarin-HSA interactions, a novel coumarin-derived near-infrared (NIR) fluorogenic sensor, NCBP, was engineered based on a twisted intramolecular charge transfer (TICT) mechanism. Under physiological conditions, NCBP rapidly and stably bound to subdomain IIA of HSA with 1:1 stoichiometry, triggering a 79-fold fluorescence enhancement at 665 nm. NCBP integrated multiple advantages for detecting HSA, including instantaneous response, high physicochemical stability, ultrahigh sensitivity, and excellent selectivity. Furthermore, NCBP enabled in situ spatiotemporal imaging of HSA reabsorption in living nephrocytes and renal tissues, which was then used for screening nephroprotective agents to mitigate cisplatin-induced nephrotoxicity (CINT). Nobiletin (NOB) and 4',7-dimethoxyisoflavone (DIF) were identified as promising lead compounds capable of restoring renal uptake function and mitigating cisplatin-induced oxidative stress. In CINT mice, both NOB and DIF significantly improved renal function and attenuated tubular injury, confirming their nephroprotective potentials. Collectively, a TICT-based NIR sensor was developed for in situ imaging of HSA reabsorption, offering a robust phenotypic platform for spatiotemporal mapping of cellular HSA trafficking and discovering nephroprotective agents.