Validation of a novel animal model for sciatic nerve repair with an adipose-derived stem cell loaded fibrin conduit

Abstract

Despite the regenerative capabilities of peripheral nerves, severe injuries or neuronal trauma of critical size impose immense hurdles for proper restoration of neuro-muscular circuitry. Autologous nerve grafts improve re-establishment of connectivity, but also comprise substantial donor site morbidity. We developed a rat model which allows the testing of different cell applications, i.e., mesenchymal stem cells, to improve nerve regeneration in vivo. To mimic inaccurate alignment of autologous nerve grafts with the injured nerve, a 20 mm portion of the sciatic nerve was excised, and sutured back in place in reversed direction. To validate the feasibility of our novel model, a fibrin gel conduit containing autologous undifferentiated adipose-derived stem cells was applied around the coaptation sites and compared to autologous nerve grafts. After evaluating sciatic nerve function for 16 weeks postoperatively, animals were sacrificed, and gastrocnemius muscle weight was determined along with morphological parameters (g-ratio, axon density & diameter) of regenerating axons. Interestingly, the addition of undifferentiated adipose-derived stem cells resulted in a significantly improved re-myelination, axon ingrowth and functional outcome, when compared to animals without a cell seeded conduit. The presented model thus displays several intriguing features: it imitates a certain mismatch in size, distribution and orientation of axons within the nerve coaptation site. The fibrin conduit itself allows for an easy application of cells and, as a true critical-size defect model, any observed improvement relates directly to the performed intervention. Since fibrin and adipose-derived stem cells have been approved for human applications, the technique can theoretically be performed on humans. Thus, we suggest that the model is a powerful tool to investigate cell mediated assistance of peripheral nerve regeneration.

Ex-Vivo Stimulation of Adipose Stem Cells by Growth Factors and Fibrin-Hydrogel Assisted Delivery Strategies for Treating Nerve Gap-Injuries

“…When co-cultured with motor neuron-like cells or dorsal root ganglion (DRG) sensory neurons, ASC enhanced the neurite number and outgrowth length [ 21 , 22 , 23 ]. In line with these findings, several animal studies reported enhanced axonal regeneration and sensory-motor nerve conduction, when ASC were transplanted in polymeric nerve conduits (NC) or fibrin-hydrogel nerve conduits (FNC) [ 24 , 25 , 26 ]. Improved axonal growth and elongation was found in the FNC loaded with ASC in comparison to empty FNC [ 24 , 27 , 28 ].…”

“…However, an optimal delivery route for ASC still remains to be established in the context of peripheral nerve reconstruction. Various studies involving ASC therapy employed different cell delivery routes, i.e., injection into the lumen, dispersion within the fibrin conduit wall, dispersion within the lumen of fibrin matrix and coating on the luminal surface [ 7 , 22 , 26 , 27 , 29 , 30 ]. However, the therapeutic efficacy of the cells was scarcely correlated with delivery routes and carrier matrix in the context of nerve regeneration.…”

Restoration of Neurological Function Following Peripheral Nerve Trauma

“…Additional techniques for enhancing axons regeneration through long allografts grafts include filling them with platelet-rich plasma (PRP) [140], autologous Schwann cells [141,142], adipose-derived mesenchymal stem cells (ADSCs), or primary Schwann cell-like differentiated bone marrow-derived mesenchymal stem cells (DMSCs) [142][143][144][145]. These cells induce enhanced axon regeneration by releasing neurotrophic factors [146,147].…”

“…Axon regeneration is extensive through conduits composed of fibrin [145,153], hydrogel tubes [154], alginate/chitosan polyelectrolyte [155][156][157], poly epsilon-caprolactone [158,159], polyglycolic acid [160], poly(lactic-co-glycolic acid) or silk-based [161][162][163][164]. Conduits composed of decellularized human umbilical artery [165] and muscles [166] are also effective in promoting axon regeneration across nerve gaps.…”

“…The efficacy of fibrin conduits is enhanced when they are filled with autologous undifferentiated adipose-derived stem cells [145] or contain mesenchymal stem cells [195], and when hydrogel conduits contain mesenchymal stem cells [196]. The efficacy of chitosan conduits is enhanced when they contain combinations of fibronectin and laminin with mesenchymal stem cells (MSCs) or Schwann cells [190], chitosan/PLGA scaffolds are combined with mesenchymal stem cells [197], and when three-dimensional alginate/chitosan conduits are filled with muscle fibers [198].…”