Development of a Fluorescent Probe for Real-Time In Vivo Imaging of Cysteine Dynamics in a Mouse Model of Lipopolysaccharide-Induced Acute Lung Injury.

Acute lung injury (ALI) involves inflammatory dysregulation and oxidative stress, processes in which cysteine (Cys), an endogenous sulfur-containing biothiol, participates through thiol redox homeostasis. We designed HD-Cys, an activatable hemicyanine probe, to visualize Cys in real-time in an LPS-induced murine ALI model. The reaction with Cys releases the emissive HD form and produces a pronounced near-infrared turn-on response. HD-Cys showed high selectivity, a detection limit of 160 nM, and a linear concentration-dependent response. Its performance was examined in BEAS-2B cells, serum, and mice with LPS-induced ALI. After probe administration, pulmonary fluorescence was stronger in ALI mice than in normal controls and decreased following N-ethylmaleimide (NEM)-mediated thiol depletion. Together, these findings establish HD-Cys as an experimental tool for tracking Cys-associated thiol redox changes during inflammatory lung injury.