Near infrared fluorophore specific for annexin A2 identifies peripheral nerve injury in a rodent transection model.

Introduction: Peripheral nerve injuries (PNI) pose a major challenge in the intraoperative assessment of nerve viability. Wallerian degeneration (WD) is the degenerative process of axonal breakdown distal to the site of injury, with limited proximal extension, and progresses through spatiotemporally consistent stages facilitated by Schwann cell reprogramming and macrophage infiltration. We evaluated LS-301, a near-infrared (NIR) fluorophore previously used in human oncology trials, that targets phosphorylated annexin A2 (pANXA2), which is upregulated and redistributed to Schwann cell surfaces after nerve injury. Methods: Utilizing a sciatic nerve transection model in rats, LS-301 was compared with the untargeted control dye Cypate-3 using in vivo fluorescence imaging. Fluorescence intensities in proximal and distal bulbs and their adjacent segments were quantified, normalized to the contralateral sham nerve, and compared across time points chosen to represent documented stages of WD (5 h, 2 days, and 2 weeks). Results: LS-301 showed time-dependent accumulation in injured nerve in a spatial pattern consistent with the expected progression of WD, whereas Cypate-3 uptake was variable and lacked a consistent spatiotemporal gradient. Discussion: This study's findings support the feasibility of using a targeted NIR probe to preferentially label degenerating versus uninjured peripheral nerve after transection, with potential for intra-operative application. This proof-of-concept study does not define per-nerve surgical decision thresholds yet, but this will be the focus of future work testing whether LS-301 mapping can complement existing intraoperative assessments and determine surgically actionable fluorescence cutoffs.