Effect Of combining FK506 and neurotrophins on neurite branching and elongation

Abstract

Introduction There is a clinical need to improve the outcomes of peripheral nerve regeneration and repair after injury. In addition to its immunosuppressive effects, FK506 (tacrolimus) has been shown to have neuroregenerative properties. To determine biologically relevant local FK506 and growth factor concentrations, we performed an in vitro bioassay using dorsal root ganglion (DRG) from chicken embryos. Methods Neurite elongation and neurite branching were analyzed microscopically after addition of FK506, glial cell line-derived neurotrophic factor (GDNF), and nerve growth factor (NGF), each alone and in combination. Results FK506 induced modest neurite elongation (~500–800 μm) without improving neurite branching significantly. The combination of FK506 with NGF, GDNF, or both, exerted a potentiating or competitive effect on neurite elongation (~700–1100 μm) based on dosage and competitive effect on neurite branching (~0.2–0.4). Conclusions These results strongly suggest that the interaction of FK506 with GDNF and NGF mediates distinct enhancement of neurite growth.

Local FK506 delivery at the direct nerve repair site improves nerve regeneration

“…Samples were diluted to lower concentrations that were previously found more optimal for neurite growth and were within the ELISA detection range. 17 LD-Wrap and HD-Wrap drug release test samples were diluted by a factor of 10 and 2, respectively. Drug release test samples average concentrations after dilution: Day 4 LD-Wrap -18.5 ng/mL FK506 and Day 4 HD-Wrap -23.1 ng/mL FK506.…”

Drug‐delivering nerve conduit improves regeneration in a critical‐sized gap

“…Sink method was used for drug collection (Labroo et al, 2017 Sink method was used for drug collection (Labroo et al, 2017 …”

“…Treatment with FK506 has been reported to enhance the rate of axonal regeneration in the rat after nerve grafting into the injured spinal cord (Wang & Gold, 1999). Based on our previous work, an increase in the activation of the AKT pathway was observed when dorsal root ganglions (DRGs) were exposed to FK506 or GDNF, as evidenced by increased protein expression of protein kinase B (AKT) and phosphorylated AKT by western blot analysis (Labroo, Shea, Sant, Gale, & Agarwal, 2017). Data suggest that FK506 or GDNF treatment enhances nerve growth through activation of the Ras/Raf/ MAP kinase signaling pathway downstream of PI3K-Akt (Price, Yamaji, & Matsuoka, 2003).…”

Advances in peripheral nerve regeneration as it relates to VCA

“…Interestingly, their study showed that FK506, given systemically for 2 months following end to end anastomosis of a transected facial nerve, resulted in a significant increase in axonal diameter, myelin sheath thickness, and a total increase in the number of myelinated axons compared with the control group. 70 Additionally, FK506 has been shown in a mouse orthotopic limb allotransplantation model to improve Schwann cell migration and proliferation as well as leading to more robust axonal regeneration.…”

“…Furthermore, nerve samples treated with a combination of FK506 and glial cell line-derived neurotrophic factors (GDNF) showed an even greater significant increase in neurite elongation and branching, which was dose dependent and occurred in the first 48 hours in vitro. 70 The same group has worked to develop drug-release devices that aim to release optimal levels of FK506 at controllable rates for improved neurite growth and outbranching, but such devices require more study to assess their efficacy and effectiveness on nerve regeneration and functional recovery. 69 While FK506 has been shown to reduce inflammation and prevent rejection, it has been shown that a component of rejection may actually be beneficial to nerve recovery.…”