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Novel Nerve Guide Containing GDNF Microspheres Improves Recovery After Facial Nerve Injury In Rats
Fuat Baris Bengur, MD, Chiaki Komatsu, MD, Jocelyn S. Baker, BS, Caroline Nadia Fedor, BA, Aanchal Totwani, BS, Shawn Loder, MD, W. Vincent Nerone, BA, Mario G. Solari, MD, Kacey G. Marra, PhD.
University of Pittsburgh, Pittsburgh, PA, USA.

PURPOSE: Injury to the facial nerve and the resulting facial nerve palsy lead to devastating functional, psychological, and cosmetic challenges. Rapid functional recovery after facial nerve injury is critical to prevent muscle atrophy and restore expression. Bioengineering plays an important role to create artificial materials that are able to mimic the nerve itself without the need for a donor nerve. Tissue engineered nerve guides support enhanced recovery, by reducing axonal sprouting, minimizing neural scar formation, and acting as regenerative scaffolds. This can be improved by addition of exogenous neuro-supportive agents such as glial-derived neurotrophic factor (GDNF). GDNF is a promoter of axonal elongation and branching and has been shown to promote Schwann cell proliferation and migration. In this study, we evaluated efficacy of a composite poly(caprolactone) nerve guide containing double-walled GDNF microspheres on functional, electrophysiological, and histological outcomes in a rat facial nerve injury model.
METHODS: GDNF was encapsulated within double-walled poly(lactic-co-glycolic acid)/poly(lactide) microspheres and embedded in the walls biodegradable poly(caprolactone) nerve guides. This nerve guide capable of providing a sustained release of GDNF for >50 days was used to repair a facial nerve injury model in male Lewis rats. After transection and primary repair of the buccal branch of the facial nerve, the rats were divided as follows: a) transection and repair only, b) empty guide, c) GDNF-guide. Marginal mandibular branch of the facial nerve was also transected and ligated to prevent innervation of the whiskers. Weekly measurements of the whisking movements for protraction, retraction and amplitude angles were recorded. At the endpoint of 12-weeks, compound muscle action potentials at the whisker pad were assessed and nerve, muscle, and whisker pad were collected for histomorphometric analysis, including Schwann cell analysis.
RESULTS: GDNF-guide treated rats displayed earliest peak and achieved the highest whisking amplitude with 36% recovery compared to the baseline. Weekly whisking amplitude measurements demonstrated both time and the treatment groups were independently associated with the recovery (p<0.001) and GDNF treatment had the highest impact versus all others (p<0.05). Compound muscle action potentials were significantly higher after GDNF-guide placement versus all others (p<0.001). Mean muscle fiber surface area at the levator labii superioris muscle was the highest (p<0.01). The axonal integrity loss was less prominent within the GDNF-guides, and the nerves demonstrated the highest mean axonal count (p<0.05). Gross morphology of the whisker pad was not different across the groups.
CONCLUSION: The novel tissue engineered nerve guide containing double-walled GDNF microspheres enhances recovery after facial nerve transection. Results support the clinical viability of these guides to enhance recovery after nerve injury and hold promise to facilitate recovery in defects with larger gaps.


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