Noninvasive In Vivo Molecular Imaging of Neutrophil Elastase

Neutrophil elastase (NE) plays a crucial role in tissue injury and immune regulation across a broad range of inflammation-associated diseases, and changes in its activity provide informative readouts for disease stratification and treatment monitoring. However, current assessments based on biofluids and histology are largely sample-dependent and static, limiting in vivo spatial localization and longitudinal tracking, and often failing to distinguish enzymatic activity from expression levels. In this review, we summarize recent advances in noninvasive in vivo molecular imaging of NE. Specifically, we outline NE-responsive and NE-targeted probes and tracers across near-infrared fluorescence imaging, photoacoustic imaging, and positron emission tomography (PET), while briefly covering representative chemiluminescence strategies as an adjunct modality. We highlight key probe design and signal-transduction strategies and synthesize representative in vivo applications in lung inflammation, cardiovascular inflammation, tumor immunology, and gastrointestinal inflammation.