Effect of FK506 nanospheres on regeneration of allogeneic nerve after transplant

Nerve Wrap for Local Delivery of FK506/Tacrolimus Accelerates Nerve Regeneration

Peripheral nerve injuries (PNIs) occur frequently and can lead to devastating and permanent sensory and motor function disabilities. Systemic tacrolimus (FK506) administration has been shown to hasten recovery and improve functional outcomes after PNI repair. Unfortunately, high systemic levels of FK506 can result in adverse side effects. The localized administration of FK506 could provide the neuroregenerative benefits of FK506 while avoiding systemic, off-target side effects. This study investigates the utility of a novel FK506-impregnated polyester urethane urea (PEUU) nerve wrap to treat PNI in a previously validated rat infraorbital nerve (ION) transection and repair model. ION function was assessed by microelectrode recordings of trigeminal ganglion cells responding to controlled vibrissae deflections in ION-transected and -repaired animals, with and without the nerve wrap. Peristimulus time histograms (PSTHs) having 1 ms bins were constructed from spike times of individual single units. Responses to stimulus onsets (ON responses) were calculated during a 20 ms period beginning 1 ms after deflection onset; this epoch captures the initial, transient phase of the whisker-evoked response. Compared to no-wrap controls, rats with PEUU-FK506 wraps functionally recovered earlier, displaying larger response magnitudes. With nerve wrap treatment, FK506 blood levels up to six weeks were measured nearly at the limit of quantification (LOQ ≥ 2.0 ng/mL); whereas the drug concentrations within the ION and muscle were much higher, demonstrating the local delivery of FK506 to treat PNI. An immunohistological assessment of ION showed increased myelin expression for animals assigned to neurorrhaphy with PEUU-FK506 treatment compared to untreated or systemic-FK506-treated animals, suggesting that improved PNI outcomes using PEUU-FK506 is mediated by the modulation of Schwann cell activity.

Local delivery of tacrolimus using electrospun poly-ϵ-caprolactone nanofibres suppresses the T-cell response to peripheral nerve allografts

Objective.Repair of nerve gap injuries can be achieved through nerve autografting, but this approach is restricted by limited tissue supply and donor site morbidity. The use of living nerve allografts would provide an abundant tissue source, improving outcomes following peripheral nerve injury. Currently this approach is not used due to the requirement for systemic immunosuppression, to prevent donor-derived cells within the transplanted nerve causing an immune response, which is associated with severe adverse effects. The aim of this study was to develop a method for delivering immunosuppression locally, then to test its effectiveness in reducing the immune response to transplanted tissue in a rat model of nerve allograft repair.Approach.A coaxial electrospinning approach was used to produce poly-ϵ-caprolactone fibre sheets loaded with the immunosuppressant tacrolimus. The material was characterised in terms of structure and tacrolimus release, then testedin vivothrough implantation in a rat sciatic nerve allograft model with immunologically mismatched host and donor tissue.Main results.Following successful drug encapsulation, the fibre sheets showed nanofibrous structure and controlled release of tacrolimus over several weeks. Materials containing tacrolimus (and blank material controls) were implanted around the nerve graft at the time of allograft or autograft repair. The fibre sheets were well tolerated by the animals and tacrolimus release resulted in a significant reduction in lymphocyte infiltration at 3 weeks post-transplantation.Significance.These findings demonstrate proof of concept for a novel nanofibrous biomaterial-based targeted drug delivery strategy for immunosuppression in peripheral nerve allografting.

Local FK506 drug delivery enhances nerve regeneration through fresh, unprocessed peripheral nerve allografts

OBJECTIVE

Nerve allografts offer many advantages in the reconstruction of peripheral nerve gaps: they retain their native microstructure, contain pro-regenerative Schwann cells, are widely available, and avoid donor site morbidity. Unfortunately, clinical use of nerve allografts is limited by the need for systemic immunosuppression and its adverse effects. To eliminate the toxicity of the systemic immunosuppressant FK506, we developed a local FK506 drug delivery system (DDS) to provide drug release over 28 days. The study objective was to investigate if the local FK506 DDS enhances nerve regeneration in a rodent model of nerve gap defect reconstruction with immunologically-disparate nerve allografts.

METHODS

In male Lewis rats, a common peroneal nerve gap defect was reconstructed with either a 20 mm nerve isograft from a donor Lewis rat or a 20 mm fresh, unprocessed nerve allograft from an immunologically incompatible donor ACI rat. After 4 weeks of survival, nerve regeneration was evaluated using retrograde neuronal labelling, quantitative histomorphometry, and serum cytokine profile.

RESULTS

Treatment with both systemic FK506 and the local FK506 DDS significantly improved motor and sensory neuronal regeneration, as well as histomorphometric indices including myelinated axon number. Rats with nerve allografts treated with either systemic or local FK506 had significantly reduced serum concentrations of the pro-inflammatory cytokine IL-12 compared to untreated vehicle control rats with nerve allografts. Serum FK506 levels were undetectable in rats with local FK506 DDS.

INTERPRETATION

The local FK506 DDS improved motor and sensory nerve regeneration through fresh nerve allografts to a level equal to that of either systemic FK506 or nerve isografting. This treatment may be clinically translatable in peripheral nerve reconstruction or vascularized composite allotransplantation.