Intraoperative Real-Time Fluorescence Labeling of Degenerated Facial Nerves with Bevonescein.

OBJECTIVES

Bevonescein (ALM-488), a nerve-targeted peptide-dye conjugate, enables intraoperative fluorescence of degenerated peripheral nerves due to its extracellular matrix-binding mechanism. In contrast, myelin-based nerve-targeting agents would not be expected to label degenerated nerves due to demyelination. We compare the intraoperative fluorescence of chronically degenerated murine facial nerves produced by bevonescein and myelin-binding dye oxazine-4 and discuss its utility in peripheral nerve reconstruction.

METHODS

Sixteen wild-type mice underwent transection of the marginal mandibular branch of the facial nerve. At five months, ten mice were co-injected with bevonescein and oxazine-4 and underwent intraoperative facial nerve exploration with fluorescence imaging. Signal-to-background ratio (SBR) was calculated by comparing the mean gray value along each nerve segment to adjacent non-nerve tissue.

RESULTS

All degenerated nerve segments were visible with bevonescein (100%, n=20 nerves, 10 mice). In contrast, degenerated segments were invisible with oxazine-4 in 6/10 mice (60%, n=12 nerves, 10 mice) and faintly perceptible in 4/10 mice (40%, n = 8 nerves, 10 mice). The mean SBR for oxazine-4 was lower than bevonescein (1.27±0.54 vs 3.31±1.11, p<0.001). Autonomic nerves demonstrated strong fluorescence with bevonescein (SBR = 1.77±0.65; n=7 nerves, 7 mice) but were invisible or faintly visible with oxazine-4 (SBR = 1.11±0.14; n=7 nerves, 7 mice; p=0.02).

CONCLUSIONS

Bevonescein produces successful intraoperative labeling of chronically degenerated and autonomic nerves in a rodent nerve transection model. In contrast, myelin-binding oxazine-4 does not meaningfully produce fluorescence labeling in these contexts. These findings may influence choice of nerve-labeling agents in the setting of delayed peripheral nerve construction.

CLINICAL RELEVANCE STATEMENT

This study demonstrates the utility of bevonescein, a fluorescein-conjugated nerve-binding peptide, in the identification of degenerated facial nerves during fluorescence-guided surgery. This technology could benefit reconstructive surgeons who perform delayed peripheral nerve reconstruction.

LEVEL OF EVIDENCE