Comparing electrical stimulation and tacrolimus (FK506) to enhance treating nerve injuries

Abstract

Introduction: Neuroenhancing therapies are desired because repair of nerve injuries can fail to achieve recovery. We compared two neuroenhancing therapies, electrical stimulation (ES) and systemic tacrolimus (FK506), for their capabilities to enhance regeneration in the context of a rat model.

Methods: Rats were randomized to four groups: ES 0.5 mA, ES 2.0 mA, FK506, and repair alone. All groups underwent tibial nerve transection and repair, and outcomes were assessed by using twice per week walking track analysis, cold allodynia response, relative muscle mass, and nerve histology.

Results: Electrical stimulation and FK506 groups demonstrated improved functional recovery and myelinated axon counts distal to the repair compared with repair alone. Electrical stimulation provided improvements in nerve regeneration that were not different from optimized FK506 systemic administration.

Discussion: Providing ES after nerve repair improved regeneration and recovery in rats, with minimal differences in therapeutic efficacy to FK506, further demonstrating its clinical potential to improve management of nerve injuries.

Keywords: FK506; electrical stimulation; functional recovery; peripheral nerve; regeneration; tacrolimus; tibial nerve.

Conflict of interest statement

CONFLICT OF INTEREST

The authors declare no competing financial interests. No personal compensation was provided. Checkpoint Surgical, Inc did not influence or affect the experimental design or outcome of this study.

© 2019 Wiley Periodicals, Inc.

Figures

FIGURE 1

Representative histological sections obtained 3 days after 1-hour electrical stimulation (ES) of healthy nerve. Uninjured tibial nerve was harvested 3 days after ES to evaluate whether there was any damage to nerve due to the 1-hour ES protocol. A, ES 0.5 mA. B, ES 2.0 mA. C, No ES (uninjured). Toluidine blue counterstained nerve cross-sections show myelinated axons in all groups where no detectable changes to axons or myelin are observed after ES. Scale bars = 20 μm [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Recovery after tibial nerve injury and repair measured by using walking track analysis. From walking tracks, the tibial functional index (TFI) was calculated to compare the motor recovery in each group. A more negative TFI value indicates worse function. A, Both electrical stimulation (ES) groups and tacrolimus (FK506) had increased TFI values compared with repair alone by day 25. B, Scatter plot of data at the day 42 end point. All data are mean ± SD, n = 9 per group. *P < .05 between ES 0.5 mA and repair alone, ^P < .05 between ES 2.0 mA and repair alone, #P < .05 between FK506 and repair alone [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

Outcomes 6 weeks after tibial nerve injury and repair. A, Both electrical stimulation (ES) groups and the tacrolimus (FK506) group demonstrated increased cold allodynia response time compared with uninjured nerve. No significant differences in cold allodynia response time were observed between the experimental groups. Uninjured nerve data are represented by dotted lines (mean in black and SD in grey) *P < .05. B, Only the FK506 group showed increased relative muscle mass compared with repair alone group. *P < .05 vs repair alone group. All data are mean ± SD, n = 9 per group [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 4

Representative histological sections obtained 3 weeks after surgery. Distal nerve was assessed 5 mm from the tibial nerve repair site from the following groups: A, Repair alone. B, Tacrolimus (FK506). C, Electrical stimulation (ES) at 0.5 mA. Toluidine blue counterstained nerve cross-sections show myelinated axons in all groups, but the repair alone group contained the fewest myelinated axons. Scale bars = 20 μm [Color figure can be viewed at wileyonlinelibrary.com]